GATE 2014

Smart Grid Communications

Solutions for powerline, wireless, and serial communications (Maxim, www.maxim-ic.com/communications)

Overview

An electricity grid without adequate communications is simply a power “broadcaster.” It is through the addition of two-way communications that the power grid is made “smart.”

Smart grid communications enables utilities to achieve three key objectives: intelligent monitoring, security, and load balancing. Using two-way communications, data can be collected from sensors and meters located throughout the grid and transmitted directly to the grid operator’s control room. This added communications capability provides enough bandwidth for the control room operator to actively manage the grid.

The communications must be reliable, secure, and low cost. The sheer scale of the electrical grid network makes cost a critical consideration when implementing a communications technology. Selecting a solution that minimizes the number of modems and concentrators needed to cover the entire system can dramatically reduce infrastructure costs.

At the same time, the selected technology must have enough bandwidth to handle all data traffic being sent in both directions over the grid network.

Communications networks and protocols

Communications in the smart grid can be broken into three segments:

Wide area network (WAN)

It covers long-haul distances from the command center to local neighborhoods downstream.

Neighborhood area network (NAN)

It manages all information between the WAN and the home area network using medium-voltage lines.

Home area network (HAN)

It extends communication to endpoints within the end-user home or business.

Each segment is interconnected through a node or gateway: a concentrator between the WAN and NAN and an e-meter between the NAN and HAN. Each of these nodes communicates through the network with adjacent nodes. The concentrator aggregates the data from the meters and sends that information to the grid operator.

The e-meter collects the power-usage data of the home or business by communicating with the home network gateway or functioning as the gateway itself.

The smart grid communications architecture

Each segment can utilize different communications technologies and protocols depending on the transmission environments and amount of data being transmitted. In addition to the architecture choice between wireless and powerline communications (PLC), there are a variety of wireless and PLC protocols to choose among (Table 1).

Network	Protocol	Advantages	Disadvantages	Recommendation
WAN	Wireless (2G/3G/LTE cellular, GPRS)	Extensive cellular infrastructure is readily available; large amount of aggregated data can be communicated over a long haul	Utility must rent the infrastructure from a cellular carrier for a monthly access fee; utility does not own infrastructure	Wireless usually works best
HAN	Wireless ISM	Long range; leaps transformers	Currently proprietary; dead spots complicate installation and maintenance	Useful in some topologies, such as in the U.S.
	IEEE® 802.15.4g	Long range; leaps transformers	Not yet an accepted standard	Useful in some topologies
	ZigBee®	Low cost; low power consumption allows battery operation; well-known standard	Low data rate; very short range; does not penetrate structures well	Unlikely to be used in NANs
	First generation PLC (FSK, Yitran, Echelon®)	Low cost	Unreliable; low bandwidth	Bandwidth and reliability inadequate for the smart grid
	Early generation narrowband OFDM	Better range, bandwidth, and reliability than FSK	Does not cross transformers; does not coexist with first-generation PLC	Not recommended for new designs due to cost and compatibility concerns
	Broadband PLC	High data rate	Does not cross transformers	Increases infrastructure cost, making it too costly for most large-scale deployments
	G3-PLC	Highly reliable long-range transmission; crosses transformers, reducing infrastructure costs; data rate supports frequent two-way communications; coexists with FSK; open standard; supports IPv6	Not yet an accepted standard	Excellent for NAN worldwide
HAN	ZigBee	Well-known standard that offers low cost and low power	Very short range; does not penetrate structures well	Well suited for communication between water and gas meters
	Wi-Fi®	Popular technology with high data rates	Medium range; does not penetrate cement buildings or basements	Good for consumer applications, but no provisions for meeting utility objectives
	First-generation PLC (FSK, Yitran, Echelon)	Low cost	Not reliable in home environments	Unlikely to be used in homes due to high levels of interference
	Early generation narrowband OFDM	Better range, bandwidth, and reliability than FSK	Does not cross transformers; does not coexist with first-generation PLC	Not recommended for new designs due to cost and compatibility concerns
	Broadband PLC	High bandwidth	Short range is not sufficient for NAN	Good for consumer applications, but no provisions for meeting utility objectives
	G3-PLC	Highly reliable; sufficient data rate; IPv6 enables networking with many devices	Not yet an accepted standard	Excellent for HAN worldwide

The WAN is the communications path between the grid operator and the concentrator. The WAN can be implemented over fiber or wireless media using Ethernet or cellular protocols, respectively.

Cellular or WiMAX® is most commonly used between the grid operator and the concentrator. The NAN is the path between the concentrator and the meter. It uses either wireless or PLC. Typically, the concentrator communicates with anywhere from a few to hundreds of meters, depending on the grid topology and the communications protocol used.

Today, there is no standard for this portion of the network, so most implementations use proprietary wireless or PLC technologies. Several standards bodies are currently working with utilities and technology providers to define standards for wireless and PLC protocols.

The IEEE 802.15.4g standard targets wireless; the IEEE P1901, OPEN meter, and ITU-T G.hnem standards are being developed for PLC (Table 2).

Region	WAN	NAN	HAN
North America	Cellular, WiMAX	G3-PLC, HomePlug®, IEEE 802.15.4g, IEEE P1901, ITU-T G.hnem, proprietary wireless, Wi-Fi	G3-PLC, HomePlug, ITU-T G.hn, Wi-Fi, ZigBee, Z-Wave
Europe	Cellular	G3-PLC, IEEE P1901, ITU-T G.hnem, PRIME, Wi-Fi	G3-PLC, HomePlug, ITU-T G.hn, Wi-Fi, Wireless M-Bus, ZigBee
China	Cellular, band translated WiMAX	G3-PLC, RS-485, wireless to be determined	G3-PLC, RS-485, Wi-Fi, to be determined
Rest of the World	Cellular, WiMAX	G3-PLC, HomePlug, IEEE 802.15.4g, IEEE P1901, ITU-T G.hnem, PRIME, RS-485, Wi-Fi	G3-PLC, HomePlug, ITU-T G.hn, RS-485, Wi-Fi, Wireless M-Bus, ZigBee, Z-Wave

The HAN is used by utilities to extend the reach of their communication path to devices inside the home. This network can support functions such as cycling air conditioners off during peak load conditions, sharing consumption data with in-home displays, or enabling a card-activated prepayment scheme.

The arrival of electric/plug-in hybrid electric vehicles (EV/PHEVs) presents a special communications scenario for HANs.

Standards bodies are defining PLC protocols for communicating with vehicle charging systems. In addition to supporting the data requirements for smart grid activities, a HAN might also include: peer-to-peer (P2P) communications between devices inside the home; communications with handheld remote-control devices, lighting controls, and gas or water meters; as well as broadband traffic.

Protocols such as RS-485, ZigBee, Z-Wave®, and HomePlug are used for this network. If there is a separate home gateway, it is possible that additional protocols could be used to communicate with appliances, thermostats, and other devices.

Communications alternatives in the HAN can often coexist, but utility support will probably be limited to technologies needed to support the utility’s primary objectives.

Resource: Maxim (solutions for powerline, wireless, and serial communications); www.maxim-ic.com/communications

High Voltage Testing - DC Test

DC Tests

DC tests are used mainly to do “pressure tests” on high voltage cables. Although the cables operate with AC, AC testing is not practical.

The high capacitance of the cables necessitates AC test sets with a high kVA rating to be able to supply the capacitive current. In the case of DC, once the cable is charged, only the losses have to be supplied.

DC test sets usually consist of half wave rectification, using HV selenium rectifiers.

Typical DC test set-up is shown in Figure 1.

Figure 1 - Typical circuit for DC tests

An AC high voltage test transformer is again supplied via a variac and a rectifier is used together with a filter capacitor C to limit the ripple to acceptable values. The earthing switch ES is a safety feature and closes automatically when the power is switched off to discharge the capacitor C.

Note that the peak inverse voltage required of the rectifier is 2 Vm.

Figure 2 - Typical doubling circuit for DC tests

Doubling and multiplier circuits (as used in TV’s and household appliances) are also used to obtain an even higher voltage. A typical Cockcroft-Walton (in Germany: Greinacher) doubling circuit is shown in Figure 2.

Figure 3 - Typical waveforms and a typical doubling circuit DC test source

Conductor Types Used For Overhead Lines

Conductor Types Used For Overhead Lines

Aluminium and its alloys conductor steel reinforced

The international standards covering most conductor types for overhead lines are IEC 61089 (which supersedes IEC 207, 208, 209 and 210) and EN 50182 and 50183 (see Table 1).

For 36 kV transmission and above both aluminium conductor steel reinforced (ACSR) and allaluminium alloy conductor (AAAC) may be considered. Aluminium conductor alloy reinforced (ACAR) and all aluminium alloy conductors steel reinforced (AACSR) are less common than AAAC and all such conductors may be more expensive than ACSR.

Relevant national and international standards

Standard	Title	Comment
IEC 61089	Round wire concentric lay overhead electrical stranded conductors	Supersedes IEC 207 (AAC), 208 (AAAC), 209 (ACSR) and 210 (AACSR)
EN 50182	Conductor for overhead lines: round wire concentric lay stranded conductor	Supersedes IEC 61089 for European use. BSEN 50182 identical
EN 50183	Conductor for overhead lines: aluminium–magnesium–silicon alloy wires
BS 183	Specification for general purpose galvanized steel wire strand	For earth wire
BS 7884	Specification for copper and copper–cadmium conductors for overhead systems

Historically ACSR has been widely used because of its mechanical strength, the widespread manufacturing capacity and cost effectiveness.

For all but local distribution, copper-based overhead lines are more costly because of the copper conductor material costs. Copper (BS 7884 applies) has a very high corrosion resistance and is able to withstand desert conditions under sand blasting.

All aluminium conductors (AAC) are also employed at local distribution voltage levels.

From a materials point of view the choice between ACSR and AAAC is not so obvious and at larger conductor sizes the AAAC option becomes more attractive. AAAC can achieve significant strength/weight ratios and for some constructions gives smaller sag and/or lower tower heights. With regard to long-term creep or relaxation, ACSR with its steel core is considerably less likely to be affected.

Jointing does not impose insurmountable difficulties for either ACSR or AAAC types of conductor as long as normal conductor cleaning and general preparation are observed. AAAC is slightly easier to joint than ACSR.

Figure 1 illustrates typical strandings of ACSR. The conductor, with an outer layer of segmented strands, has a smooth surface and a slightly reduced diameter for the same electrical area.

Figure 1 - Conductor arrangements for different CSR combinations

Historically there has been no standard nomenclature for overhead line conductors, although in some parts of the world code names have been used based on animal (ACSR – UK), bird (ACSR – North America), insect (AAAC – UK) or flower (AAAC – North America) names to represent certain conductor types.

Aluminium-based conductors have been referred to by their nominal aluminium area. Thus, ACSR with 54 Al strands surrounding seven steel strands, all strands of diameter d 3.18 mm, was designated 54/7/3.18; alu area 428.9 mm², steel area 55.6 mm² and described as having a nominal aluminium area of 400 mm².

In France, the conductor total area of 485 mm² is quoted and in Germany the aluminium and steel areas,429/56, are quoted. In Canada and USA, the area is quoted in circular mils (1000 circular mils 0.507 mm²).

Within Europe standard EN50182 has coordinated these codes while permitting each country to retain the actual different conductor types via the National Normative Aspects (NNAs).

Table below explains the EN 50182 designation system.

Conductor designation system to EN50182:2001

1. A designation system is used to identify stranded conductors made of aluminium with or without steel wires.
2. Homogeneous aluminium conductors are designated ALx, where x identifies the type of aluminium. Homogeneous aluminium-clad steel conductors are designated yzSA where y represents the type of steel (Grade A or B, applicable to class 20SA only), and z represents the class of aluminium cladding (20, 21, 30 or 40).
3. Composite aluminium/zinc coated steel conductors are designated ALxISTyz, where ALx identifies the external aluminium wires (envelope), and STyz identifies the steel core. In the designation of zinc coated steel wires, y represents the type of steel (Grades 1 to 6) and z represents the class of zinc coating (A to E).
4. Composite aluminium/aluminium-clad steel conductors are designated ALxIyzSA, where ALx identifies the external aluminium wires (envelope), and yzSA identifies the steel core as in 2.
5. Conductors are identified as follows:
1. A code number giving the nominal area, rounded to an integer, of the aluminium or steel as appropriate;
2. A designation identifying the type of wires constituting the conductor. For composite conductors the first description applies to the envelope and the second to the core.

The development of ‘Gap type’ heat-resistant conductors offers the possibility of higher conductor temperatures.

The design involves an extra high strength galvanized steel core, and heat-resistant aluminium alloy outer layers, separated by a gap filled with heat-resistant grease. To maintain the gap, the wires of the inner layer of the aluminium alloy are trapezoid shaped. Depending on the alloys used, temperatures of up to 210°C are possible, with a current carrying capacity of up to twice that of hard-drawn aluminium.

This offers particular value where projects involve upgrading existing circuits.

Why Lamp Flickers Sometimes

Why Lamp Flickers Sometimes

Voltage regulation

Voltage regulation has been one of the most important problems of the electric industry since its inception. The sizes of many parts of a power system are determined largely by this one consideration alone.

Large proportion of the selling price of electrical power is the interest and other fixed charges on production and distribution facilities, so that any improvement in regulation is ultimately reflected in higher rates.

Similarly, types of load imposing exceptionally severe regulation requirements will also increase the cost of supplying energy.

In the early days of the industry, a relatively wide range of voltage variation was permissible, because the public was at that time unaccustomed to uniform lighting intensity. Today, there is a greater consciousness as to whether the voltage level is about right, as indicated by the “whiteness” of the light and by lamp life.

While, however, a narrower voltage band is required than formerly, this is not always the limiting factor in voltage regulation. fSumerous new devices have been added to power lines in the last few years, which impose rapid and frequent changes of load, with correspondingly rapid voltage changes.

Repeated observations have shown that rapid changes of voltage are much more annoying than slow ones, so that “flicker” effects may limit the useful load-carrying ability of individual circuits long before maximum steady-state regulation or heating is reached.

Consequently, the voltage regulation problem must now he considered from two angles:

1. The normal drop in voltage from light load to full load, and
2. The superimposed flickers due to motor-starting and to various pulsating and irregular loads.

The differences in voltage between light and full load affect the performance, efficiency, and life of electrical equipment.

This article considers only the flicker component of voltage regulation, and deals primarily with the reaction of the human eye to variations in electric light intensity.

Permissible Flicker

The permissible amount of flicker voltage cannot be stated concisely for several reasons.

There is first the human element; one individual may think objectionable a flicker not perceptible to another. The lighting fixture used is of considerable importance. Smaller wattage incandescent lamps change illumination more quickly upon a change of voltage than lamps with heavier filaments.

The character of the voltage change is also important.

Cyclic or rapidly recurring voltage changes are generally more objectionable than non-cyclic. On non-cyclic changes the annoyance due to the flicker is affected by the rate of change, duration of change, andfrequency of occurrence of the flicker.

These and other factors greatly complicate the problem of assigning limits to permissible flicker voltages.

Numerous investigators have studied the flicker problem. The most complete analysis is found in the report “The Visual Perception and Tolerance of Flicker” prepared by Utilities Coordinated Research, Inc. and printed in 1937, from which Figures 1 to 4 of this article are reproduced.

Figure l - Cyclic pulsation of voltage at which flicker of 115~volt tungsten filament lamp is just perceptible-derived from 1104 observations by 95 persons in field tests of 25-watt, 40-watt, and 60-watt lamps conducted by Commonwealth Edison Company.

Figure 1 above shows the cyclic pulsation of voltage at which flicker of 115 volt tungsten-filament lamp is just perceptible. Flickers as low as 1/3 volt were perceptible in 10 percent of the observations, when the rate of variation was 8 cycles per second.

In order for the variations to be perceptible in 90 percent of the observations, however, the voltage change had to be over one volt at the same frequency. The range between 6 and 12 cycles per second was the most critical.

Figure 2 - Illumination on reading matter (foot candles)

Figure 2 shows the minimum abrupt voltage dip to cause perceptible flicker in a 60-watt, 120-volt tungsten-filament lamp, as a function of intensity of illumination.

Curves are shown for 5 and 15 cycles (GO cycles per second basis) durations of voltage dip. It should be noted that abrupt voltage dips of 1.5 to 2.0 volts were perceptible.

Figure 3 - Effect of duration of transition of voltage on average threshold of perceptibility of flicker of tungsten-filament lamps

Figure 3 shows the effect of “duration of transition” of voltage on the average threshold of perceptibility of flicker for tungsten-filament lamps. This curve shows quite cIearly that whereas an abrupt change of about 1 ½ volts is perceptible, a change of 5 volts or more is necessary before voltage variations requiring several seconds for completion can he perceived.

Figures 1 to 3 are of interest in showing the perceptibilities for various classes of flicker voltages. These are not working limits, because a perceptible flicker is not necessarily an objectionable one.

Figure 4 - Recommended maximum allowable cyclic variation of voltage

Figure 4 above shows the recommended maximum allowable cyclic variation of voltages as set up by various nllthorities for their own use. The variations in these recommendations is an indication of the extent to which individual judgment enters the problem.

The curves are nevertheless an exceedingly valuable guide.

Cyclic flicker, when perceptible, is likely to be objectionable, at least to some individuals.

Isolated voltage dips, however, even if plainly perceptible, are not objectionable to the majority of individuals unless rather frequent. It can, therefore, be expected that larger variations are permissible for non-cyclic than for cyclic variations, but that the amount of tolerable dip depends upon the frequency of occurrence and the class of service.

Selection of Induction Motors for Industrial Application

Introduction

All types of industries are invariably required to install different types of electric motors as prime mover fordriving process equipment participating in their respective production line up. The continuous process of technical development has resulted into availability of highly diversified types of electric motors.

Hence, an utmost care should be exercised in selection of most appropriate type of motor consideringnumber of technical factors for each application, so that the motor would provide desired and optimum performance.

The characteristics of motors vary widely with the nature of their application and the type of duty they are expected to perform. For example, the applications like constant speed, constant torque, variable speed, continuous/intermittent duty, steep/sudden starts, frequent start/stops, etc. should be taken into consideration carefully when deciding for the type of a motor for that specific application.

Moreover, the motors are required to perform quite often under abnormal conditions during their total service life.

In view of above, an incorrect selection of motor always lands the industrial buyer into all sorts of problems, including premature failure of the motor, causing severe production curtailments.

Like one mentioned above, a number of other factors and design features like weather conditions, stringent system conditions, abnormal surroundings, hazardous area, duty cycle, motor efficiency, etc. should be considered while deciding the rating and subsequently drawing out the technical specifications of the motor.

Stator and Rotor Damages

Abnormal conditions and effects

The usual abnormal conditions encountered by the motors are given below.

1. Abnormal System Conditions

1. Voltage
1. Undervoltage
2. Overvoltage
3. Unbalance in 3-phase
4. Single phasing
5. Voltage surges
2. Frequency
1. Low frequency
2. High frequency

2. Abnormal Operating conditions

1. Locked rotor or stalled rotor
2. Reswitching/Frequent start-stops
3. Momentary interruption/Bus transfer
4. Overloading
5. Improper cable sizing

3. Environmental conditions

1. High/low ambienttemperature
2. High altitude
3. High humidity
4. Corrosive atmosphere
5. Hazardous atmosphere/surroundings
6. Exposure to steam/salt-laden air/oil vapour

4. Mechanical problems

1. Seized bearings
2. Incorrect alignment/foundation levelling
3. Incorrect fixing of coupling
4. High vibration mounting
5. External shock due to load

5. Condition at location

1. Poor ventilation
2. Dirt accumulation
3. Exposure to direct sunlight

Though, above mentioned abnormalities may prevail for short or long duration or may be transient in nature, major impact of the listed abnormal conditions is overheating of the motor along with one or several of the other effects as follows.

Change in the motor performance characteristics like drawl of more power and consequent deterioration in motor efficiency, etc.

Increase in mechanical stresses leading to:

1. Shearing of shafts
2. Damage to winding overhang
3. Bearing failures
4. Insulation failures

Increase in stator and rotor winding temperature leading to:

1. Premature failure of stator or rotor insulation (For wound rotor motor)
2. Increased fire hazard
3. Breakage of rotor bar and/or end ring (For squirrel cage motors)

All the motors encounter few or several of these abnormalities during the course of their service lives. Consideration of listed abnormal conditions at design stage greatly helps to minimise the effects of abnormal conditions to maintain a consistent performance.

Design Considerations

Following are the most important design factors required to be considered when selecting a motor for any of the diversified industrial applications.

Output in kW/HP

There are two principle limitations for selecting the motor output:

1. Mechanical limitation

The breakdown torque, which is the maximum torque that the motor can produce when operating without stalling. This is a critical design factor in motor applications, particularly for the motors subjected to occasional extreme load conditions.

Another critical factor is the locked-rotor torque, which is the maximum torque that the motor can produce during startup from steady-state condition, a critical design feature for conveyor drives.

2. Electrical limitation due to insulation provided on the motor windings

The electrical load on the motor can be imposed till the winding insulation is able to withstand the prescribed temperature rise over an ambient for that particular class of insulation. Life of the motor greatly depends on the temperature rise of the windings.

Anticipated life-span of the motor can be achieved provided it is operated at its rated output without overloading and the prescribed preventive maintenance practices are religiously followed.

Speed of the Motor

Most of the motors are directly coupled with the driven equipment where in the speed of the motor and the driven equipment will be same.

In order to meet the speed of the driven equipment, the devices like gearbox, chains or belts are introduced between motor and driven equipment. In this case, it may be necessary to provide the rotor shaft suitable for its attachment with the speed decreasing or increasing device and hence the specification should include such specific requirement.

In case a variable speed drive is to be used for the speed variation, the motor should be compatible for this specific application. The standard motor may not provide desired performance when operated via variable speed drive.

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Power Supply Voltage and Frequency Variations

Variations in the power supply parameters, i.e. voltage and frequency significantly affect overall performance of the motor. As provided in IS:325-1996, the permissible voltage variation is ±5 to ±10%, permissible frequency is 50Hz ± 3%, and permissible combined variation is ±6 %.

The effect of undervoltage is more serious than that of overvoltage.

The higher torque, resulting from overvoltage, can handle a little overload without undue heating of the winding, but only for a short duration. Continuous operation with undervoltage condition increases the current at the rate of about 20% for every 5% reduction in the supply voltage, increasing the rated copper loss.

This results into heating and prolonged temperature rise, and finally the burning of winding. During a motor start-up, the torque reduces by 10% for each 5% reduction in the supply voltage, causing more starting current and consequently more rapid heating of the
winding.

Large burned out induction motor

The motor offers reduced efficiency at either overvoltage or undervoltage. Power factor drops sharply with higher voltage and improves with lower voltage. Even when motor is lightly loaded, over-voltage cause rise in current and temperature thus reducing the life of motor. The variation in frequency by +5 % decreases the torque by about 10% and vice-versa at – 5% frequency, the torque increases by about 10%.

It is, therefore, of utmost importance to consider the combined effect of variation in voltage and frequency both when purchasing the motor.

Unbalance in the supply voltage results into a current unbalance of 6 to 10 times the percentage voltage unbalance. This in turn results into generation of negative sequence currents in the rotor causing its overheating and premature failure.

IEEE Codes – Device Designation Numbers

Introduction : 

In the design of electrical power systems, the ANSI Standard Device Numbers (ANSI /IEEE Standard C37.2) denote what features a protective device supports (such as a relay or circuit breaker). These types of devices protect electrical systems and components from damage when an unwanted event occurs, such as an electrical fault. Device numbers are used to identify the functions of devices shown on a schematic diagram.

Function descriptions are given in the standard. ANSI/IEEE C37.2-2008 is one of a continuing series of revisions of the standard, which originated in 1928.

Device Numbers

1. Master Element

is the initiating device, such as a control switch, voltage relay, float switch, etc., which serves either directly or through such permissive devices as protective and time-delay relays to place an equipment in or out of operation.

2. Time Delay Starting or Closing Relay

is a device that functions to give a desired amount of time delay before or after any point of operation in switching sequence or protective relay system, except as specifically provided by service function 48, 62, and 79.

3. Checking or Interlocking Relay

is a relay that operates in response to the position of a number of other devices (or to a number of predetermined conditions) in an equipment, to allow an operating sequence to proceed, or to stop, or to provide a check of the position of these devices or of these conditions for any purpose.

4. Master Contactor

is a device generally controlled by device function 1or the equivalent and the required permissive and protective devices, that serves to make and break the necessary control circuits to place an equipment into operation under the desired conditions and to take it out of operation under other or abnormal conditions.

5. Stopping Device

is a control device used primarily to shut down an equipment and hold it out of operation. (This device may be manually or electrically actuated, but excludes the function of electrical lockout [see device function 86] on abnormal conditions.)

6. Starting Circuit Breaker

is a device whose principal function is to connect a machine to its source of starting voltage.

7. Anode Circuit Breaker

is a device used in the anode circuits of a power rectifier for the primary purpose of interrupting the rectifier circuit if an arc-back should occur.

8. Control Power Disconnecting Device

is a disconnecting device, such as a knife switch, circuit breaker, or pull-out fuse block, used for the purpose of respectively connecting and disconnecting the source of control power to and from the control bus or equipment.

Note: control power is considered to include auxiliary power which supplies such apparatus as small motors and heaters.

9. Reversing Device

is a device that is used for the purpose of reversing a machine field or for performing any other reversing functions.

10. Unit Sequence Switch

is a switch that is used to change the sequence in which units may be placed in and out of service in multiple-unit equipments.

11. Reserved for Future Application

(USBR assigned - Control Power Transformer).

12. Over-Speed Device

is usually a direct-connected speed switch which functions on machine over-speed.

13. Synchronous-Speed Device

is a device such as a centrifugal switch, a slip-frequency relay, a voltage relay, and undercurrent relay , or any type of device that operates at approximately the synchronous speed of a machine.

14. Under-Speed Device

is a device that functions when the speed of a machine fall below a pre -determined value.

15. Speed or Frequency Matching Device

is a device that functions to match and hold the speed or frequency of a machine or of a system equal to, or approximately equal to, that of another machine, source, or system.

16. Reserved for Future Application

(USBR assigned - Battery Charging Device).

17. Shunting or Discharge Switch

is a switch that serves to open or to close a shunting circuit around any piece of apparatus (except a resistor, such as a machine field, a machine armature, a capacitor, or a reactor).

Note: This excludes devices that perform such shunting operations as may be necessary in the process of starting a machine by devices 6 or 42, or their equivalent, and also excludes device function 73 that serves for the switching of resistors.

18. Accelerating or Decelerating Device

is a device that is used to close or to cause the closing of circuits which are used to increase or decrease the speed of a machine.

19. Starting-to-Running Transition Contactor

is a device that operates to initiate or cause the automatic transfer of a machine from the starting to the running power connection.

20. Valve

is one used in a vacuum, air, gas, oil, or similar line, when it is electrically operated or has electrical accessories such as auxiliary switches.

21. Distance Relay

is a relay that functions when the circuit admittance, impedance, or reactance increases or decreases beyond predetermined limits.

22. Equalizer Circuit Breaker

is a breaker that serves to control or to make and break the equalizer or the current-balancing connections for a machine field, or for regulating equipment in a multiple -unit installation.

23. Temperature Control Device

is a device that function to raise or lower the temperature of a machine or other apparatus, or of any medium, when its temperature falls below, or rises above, a predetermined value.

Note: An example is a thermostat that switches on a space heater in a switchgear assembly when the temperature falls to a desired value as distinguished from a device that is used to provide automatic temperature regulation between close limits and would be designated as device function 90T.

24. Reserved for future Application

(USBR assigned - bus tie circuit breaker, contactor, or switch.)

25. Synchronizing or Synchronism-Check Device

is a device that operates when two a-c circuits are within the desired limits of frequency, phase angle, or voltage, to permit or to cause the paralleling of these two circuits

26. Apparatus Thermal Device

is a device that functions when the temperature of the shunt field or the amortisseur winding of a machine, or that of a load limiting or load shifting resistor or of a liquid or other medium, exceeds a predetermined value: or if the temperature of the protected apparatus, such as a power rectifier, or of any medium decrease below a predetermined value.

27. Undervoltage Relay

is a relay that functions on a given value of under-voltage.

28. Flame Detector

is a device that monitors the presence of the pilot or main flame of such apparatus as a gas turbine or a steam boiler.

29. Isolating Contactor

is a device that is used expressly for disconnecting one circuit from another for the purposes of emergency operation, maintenance, or test.

30. Annunciator Relay

is a non-automatically reset device that gives a number of separate visual indications of the functions of protective devices, and which may also be arranged to perform a lockout function.

31. Separate Excitation Device

is a device that connects a circuit, such as the shunt field of a synchronous converter, to a source of separate excitation during the starting sequence; or one that energizes the excitation and ignition circuits of a power rectifier.

32. Directional Power Relay

is a device that functions on a desired value of power flow in a given direction or upon reverse power resulting from arcback in the anode or cathode circuits of a power rectifier.

33. Position Switch

is a switch that makes or breaks contact when the main device or piece of apparatus which has no device function number reaches a given position.

34. Master Sequence Device

is a device such as a motor-operated multi-contact switch, or the equivalent, or programming device, such as a computer, that establishes or determines the operating sequence of the major devices in a equipment during starting and stopping or during other sequential switch operations.

35. Brush-Operating or Slipping Short-Circuiting Device

is a device for raising, lowering, or shifting the brushes of a machine, or for short-circuiting its slip rings, or for engaging or disengaging the contacts of a mechanical rectifier.

36. Polarity or Polarizing Voltage Device

is a device that operates, or permits the operation of, another device on a predetermined polarity only, or verifies the presence of a polarizing voltage in an equipment.

37. Undercurrent or Underpower Relay

is a relay that function when the current or power flow decreases below a predetermined value.

38. Bearing Protective Device

is a device that functions on excessive bearing temperature, or on another abnormal mechanical conditions associated with the bearing, such as undue wear, which may eventually result in excessive bearing temperature.

39. Mechanical Condition Monitor

is a device that functions upon the occurrence of an abnormal mechanical condition (except that associated with bearing as covered under device function 38), such as excessive vibration, eccentricity, expansion shock, tilting, or seal failure.

40. Field Relay

is a relay that functions on a given or abnormally low value or failure of a machine field current, or on excessive value of the reactive component of armature current in an a-c machine indicating abnormally low field excitation.

41. Field Circuit Breaker

is a device that functions to apply or remove the field excitation of a machine.

42. Running Circuit Breaker

is a device whose principal function is to connect a machine to its source of running or operation voltage. This function may also be used for a device, such as a contactor, that is used in series with a circuit breaker or other field protecting means, primarily for frequent opening and closing of the breaker.

43. Manual Transfer or Selector Device

is a manually operated device that transfers the control circuits in order to modify the plan of operation of the switching equipment or of some of the devices.

44. Unit Sequence Starting Relay

is a relay that function to start the next available unit in a multiple-unitequipment upon the failure or non-availability of the normally preceding unit.

45. Atmospheric Condition Monitor

is a device, that functions upon the occurrence of an abnormal atmospheric condition, such as damaging fumes, explosive mixtures, smoke or fire.

46. Reverse Phase or Phase Balance Current Relay

is a relay that functions when the polyphase currents are of reverse-phase sequence, or when the polyphase currents are unbalanced or contain negative phase-sequence components above a given amount.

47. Phase-Sequence Voltage Relay

is a relay that function upon a predetermined value of polyphase voltage in the desired phase sequence.

48. Incomplete Sequence Relay

is a relay that generally returns the equipment to the normal, or off, position and locks it out if the normal starting, operating, or stopping sequence is not properly completed within a predetermined time. If the device is used for alarm purposes only, it should preferably be designated as 48A (alarm).

49. Machine or Transformer Thermal Relay

is a relay that functions when the temperature of a machine armature or other load-carrying winding or element of a machine or the temperature of a power rectifier or power transformer (including a power rectifier transformer) exceeds a predetermined value.

50. Instantaneous Overcurrent or Rate -of-Rise Relay

is a relay that functions instantaneously on an excessive value of current or on an excessive rate of current rise, thus indicating a fault in the apparatus or circuit being protected.

51. A-C Time Overcurrent Relay

is a relay with either a definite or inverse time characteristic that functions when the current in an a-c circuit exceed a predetermined value.

52. A-C Circuit Breaker

is a device that is used to close and interrupt an a-c power circuit under normal conditions or to interrupt this circuit under fault of emergency conditions.

53. Exciter or D-C Generator Relay

is a relay that forces the d-c machine field excitation to build up during starting or which functions when the machine voltage has been built up to a given value.

54. High-Speed D-C Circuit Breaker

is a circuit breaker which starts to reduce the current in the main circuit in 0.01 second or less, after the occurrence of the d-c overcurrent or the excessive rate of current rise.

55. Power Factor Relay

is a relay that operates when the power factor in an a-c circuit rises above or falls below a predetermined value.

56. Field Application Relay

is a relay that automatically controls the application of the field excitation to an a-c motor at some predetermined point in the slip cycle.

57. Short-Circuiting or Grounding Device

is a primary circuit switching device that functions to short-circuit or to ground a circuit in response to automatic or manual means.

58. Rectification Failure Relay

is a device that functions if one or mote anodes of a power rectifier fail to fire, or to detect and arc-back or on failure of a diode to conduct or lock properly.

59. Overvoltage Relay

is a relay that functions on a given value of over-voltage.

60. Voltage or Current Balance Relay

is a relay that operates on a given difference in voltage, or current input or output, or two circuits.

61. Reserved for Future Application.

62. Time-Delay Stopping or Opening Relay

is a time-delay relay that serves in conjunction with the device that initiates the shutdown, stopping, or opening operation in an automatic sequence or protective relay system.

63. Liquid or Gas Pressure or Vacuum Relay

is a relay that operates on given values of liquid or gas pressure or on given rates of change of these values.

64. Ground Protective Relay

is a relay that functions on failure of the insulation of a machine, transformer, or of other apparatus to ground, or on flashover of a d-c machine to ground.

Note: This function is assigned only to a relay that detects the flow of current from the frame of a machine or enclosing case or structure of piece of apparatus to ground, or detects a ground on a normally ungrounded winding or circuit. It is not applied to a device connected in the secondary circuit of current transformer, in the secondary neutral of current transformers, connected in the power circuit of a normally grounded system.

65. Governor

is the assembly of fluid, electrical, or mechanical control equipment used for regulating the flow of water, steam, or other medium to the prime mover for such purposes a starting, holding speed or load, or stopping.

66. Notching or Jogging Device

is a device that functions to allow only a specified number of operations of a given device or equipment, or a specified number of successive operations within a given time of each other. It is also a device that functions to energize a circuit periodically or for fractions of specified time intervals, or that is used to permit intermittent acceleration or jogging of a machine at low speeds for mechanical positioning.

67. A-C Directional Overcurrent Relay

is a relay that functions on a desired value of a-c over-current flowing in a predetermined direction.

68. Blocking Relay

is a relay that initiates a pilot signal for blocking of tripping on external faults in a transmission line or in other apparatus under predetermined condition, or cooperates with other devices to block tripping or to block re-closing on an out-of-step condition or on power savings.

69. Permissive Control Device

is generally a two-position, manually-operated switch that, in one position, permits the closing of a circuit breaker, or the placing of an equipment into operation, an in the other position prevents the circuit breaker or the equipment from being operated.

70. Rheostat

is a variable resistance device used in an electric circuit, which is electrically operated or has other electrical accessories, such a auxiliary , position, or limit switches.

71. Liquid or Gas-Level Relay

is a relay that operates on given values of liquid or gas level or on given rates of change of these values.

72. D-C Circuit Breaker

is a circuit breaker that is used to close and interrupt a d-c power circuit under normal conditions or to interrupt this circuit under fault or emergency conditions.

73. Load-Resistor Contactor

is a contactor that is used to shunt or insert a step of load limiting, shifting, or indicating resistance in a power circuit, or to switch a space heater in circuit, or to switch a light or regenerative load resistor, a power rectifier, or other machine in and out of circuit.

74. Alarm Relay

is a relay other than an annunciator, as covered under device function 30, that is used to operate, or to operate in connection with, a visual or audible alarm.

75. Position Changing Mechanism

is a mechanism that is used for moving a main device from one position to another in an equipment: as for example, shifting a removable circuit breaker unit to and from the connected, disconnected, and test positions.

76. D-C Overcurrent Relay

is a relay that function when the current in a d-c circuit exceeds a given value.

77. Pulse Transmitter

is used to generate and transmit pulses over a telemetering or pilot-wire circuit to the remote indicating or receiving device.

78. Phase-Angle Measuring or Out-Of-Step Protective Relay

is a relay that functions at a pre-determined phase angle between two voltages or between two currents or between a voltage and current.

79. A-C Reclosing Relay

is a relay that controls the automatic reclosing and locking out of an a-c circuit interrupter.

80. Liquid or Gas Flow Relay

is a relay that operates on given values of liquid or gas flow or on given rates of change of these values.

81. Frequency Relay

is a relay that functions on a predetermined value of frequency (either under or over or on normal system frequency) or rate of change of frequency.

82. D-C Reclosing Relay

is a relay thast controls the automatic closing and re-closing of a d-c circuit interrupter, generally in response to load circuit conditions.

83. Automatic Selective Control or Transfer Relay

is a relay that operates to select automatically between certain sources or conditions in a equipment, or performs a transfer operation automatically.

84. Operating Mechanism

is the complete electrical mechanism or servomechanism, including the operating motor, solenoids, position switches, etc., for a tap changer, induction regulator, or any similar piece of apparatus which otherwise has no device function number.

85. Carrier or Pilot-Wire Receiver Relay

is a relay that is operated or restrained by a signal used in connection with carrier-current or d-c pilot-wire fault directional relaying.

86. Locking-Out Relay

is an electrically operated hand, or electrically reset relay or device that functions to shut down or hold an equipment out of service, or both, upon the occurrence of abnormal conditions.

87. Differential Protective Relay

is a protective relay that functions on a percentage or phase angle or other quantitative difference of two currents or of some other electrical quantities.

88. Auxiliary Motor or Motor Generator

is one used for operating auxiliary equipment, such as pumps, blowers, exciters, rotating magnetic amplifiers, etc.

89. Line Switch

is a switch used as a disconnecting, load-interrupter, or isolating switch in an a-c or d-c power circuit, when this device is electrically operated or has electrical accessories, such as an auxiliary switch, magnetic lock, etc.

90. Regulating Device

is a device that functions to regulate a quantity, or quantities, such as voltage, current power, speed, frequency, temperature, and load at a certain value or between certain (generally close) limits for machines, tie lines, or other apparatus.

91. Voltage Directional Relay

is a device which operates when the voltage across an open circuit breaker or contactor exceeds a given value in a given direction.

92. Voltage and Power Directional Relay

is a relay that permits or causes the connection of two circuits when the voltage difference between them exceed a given value in a predetermined direction and causes these two circuits to be disconnected from each other when the power flowing between them exceeds a given value in the opposite direction.

93. Field-Changing Contactor

is a contactor that functions to increase or decrease, in one step, the value of field excitation on a machine.

94. Tripping or Trip-Free Relay

is a relay that function to trip a circuit breaker, contactor or equipment, or to permit immediate tripping by other devices; or to prevent immediate re -closure of a circuit interrupter if it should open automatically even though its closing circuit is maintained closed.

95.* (USBR assigned - Closing Relay or Contactor)

96.*

97.*

98.* (USBR assigned - Loss of Excitation Relay)

99.* (USBR assigned - Arc Detector)

Used only for specific applications in individual installations where none of the assigned numbered functions from 1 to 94 are suitable.

Auxiliary Devices

These letters denote separate auxiliary devices, such as:

• C - Closing Relay or Contactor
• CL - Auxiliary Relay, Closed (energized when main device is in closed position).
• CS - Control Switch
• D - “Down” Position Switch or Relay
• L - Lowering Relay
• 1. - Opening Relay
• OP - Auxiliary Relay, Open (energized when main device is in open position).
• PB - Push Button
• R - Raising Relay
• U - “Up” Position Switch or Relay
• X - Auxiliary Relay
• Y - Auxiliary Relay
• Z - Auxiliary Relay

Note: In the control of a circuit breaker with an X-Y Relay Control Scheme, the X relay is the device whose main contacts are used to energized the closing coil or the device which in some other manner, such as by the release of stored energy, causes the breaker to close. The contacts of the Y relay provide the anti-pump feature for the circuit breaker.