Ansi mv tech_topics43_en
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The document discusses requirements for selecting interposing relays used in remote control of circuit breakers. It provides guidelines on ensuring interposing relay contacts can make and carry coil currents without needing to interrupt them. The contacts only need to carry current for the tens of milliseconds it takes for the circuit breaker to operate. Typical interposing relays and a control scheme are presented, with notes on matching relay pickup voltages and ensuring long enough signal durations.
Ansi mv tech_topics43_en
- 1. www.usa.siemens.com/techtopics TechTopics No. 43 Interposing relay requirements Answers for infrastructure. A few salient points extracted from ANSI/IEEE C37.90 are: 5.7.1 Tripping output performance requirements: “Tripping output circuits shall meet the following specification for performance: The contacts or output circuit shall make and carry 30 A for at least 2000 operations in a duty cycle... The load shall be resistive for both dc and ac and the current shall be interrupted by independent means…” 5.7.2 Continuous and interrupting ratings of tripping output circuits: “Tripping output contacts intended by the manufacturer to be for tripping duty only shall be identified as such and may have no continuous or interrupting duty…” The requirement in ANSI/IEEE C37.90 for a making capability of 30 A is appropriate for older design circuit breakers. However, the operating currents of modern circuit breakers are often much lower than those of the historic designs, as indicated in the table for the type GMSG circuit breaker above. Remote control of circuit breakers is becoming much more prevalent as the use of monitoring and central control equipment grows. When remote control is used, interposing relays are generally required to avoid a large voltage drop in the close and trip coil circuits. Here are a few thoughts on the proper selection of interposing relays. Current ratings Interposing relay contacts used in close and trip circuits must have the ability to make and carry the current of the close and trip coils. For our type GMSG circuit breakers, the control current data is as follows: The interposing relay contact is directly analogous to a tripping output contact on a protective relay, so it is instructive to review the requirements of ANSI/IEEE C37.90 for tripping output contacts of protective relays. Control voltage and current Nominal rated control voltage Control voltage range Close coil current (A) Trip coil current (A) Close Trip 48 Vdc 38-56 28-56 2.9 11.4/301 125 Vdc 100-140 70-140 1.0 4.8/7.41 250 Vdc 200-280 140-280 0.5 2.1/4.21 120 Vac 104-127 104-127 0.9 --- 240 Vac 208-254 208-254 0.4 --- Footnote: 1 First value is for five-cycle (83 ms) rated interrupting time, second value is for three-cycle (50 ms) rated interrupting time.
- 2. The philosophy embodied in ANSI/IEEE C37.90 is appropriate for the application to tripping of circuit breakers, and similar logic applies to application of interposing relays in closing circuits. The interposing relay has to have a making capability, but does not have to have a significant interrupting capacity. This is so because the close and trip coil currents are interrupted by the “a” or “b” switch contacts on the circuit breaker. Therefore, the interposing relay should be able to make the current of the close or trip coil of the circuit breaker. The contacts also need to be able to carry the current for the time necessary for circuit breaker operation, but this is not a severe requirement. The duration of the closing or tripping current with modern circuit breakers is several tens of milliseconds, so the relay is not required to carry the current for a long time. The interposing relay contacts do not need to be able to interrupt the coil currents. Typical interposing relays A wide variety of relays are suitable for use in interposing relay applications. The most extensively-used relays over the decades are the GE type HFA and Westinghouse (ABB) type SG relays. These are older designs, and take somewhat more space than newer relays, but have a long record of success. More recently, a number of smaller relays have been used for interposing applications. Among these are relays from Potter Brumfield (KRP), Struthers Dunn (219) and even some of the miniature (“ice cube”) relays from several suppliers. Any of these relays are suitable provided they meet the voltage and current requirements of the application. Typical control scheme The basic elements of typical controls are shown in the schematic diagram. A few observations on the control scheme: Interposing relays are connected to the same control voltage supply as is used for the circuit breaker. Many contacts used to initiate remote closing or tripping, particularly PLC contacts, cannot handle the higher control voltages (e.g., 125 Vdc) used in the circuit breaker control scheme. In such cases, the interposing relay coil should be connected to the lower control voltage of the PLC (typically, 24 Vdc), and actuated by the contact from the PLC. The interposing relay output contact should be connected in the circuit breaker control circuit. Interposing relay contacts must provide a signal duration of at least 50 ms. Latched-type relays must not be used. Maintained contacts must never be used to actuate a circuit breaker close or trip circuit. The interposing relay coil should have a very low operating current, to minimize voltage drop in the control circuit from the remote actuating contact to the interposing relay coil. The minimum pickup voltage for the interposing relay must be compatible with the minimum control voltage specified in ANSI/IEEE standards for the switchgear. For dc tripping circuits, the control voltage range in ANSI/IEEE C37.06 is 56 percent to 112 percent of the rated voltage. For example, the range for 125 Vdc circuits is 70 to 140 Vdc. In contrast, the control voltage range given in ANSI/IEEE C37.90 for protective relays is 80 percent to 112 percent of rated voltage, or 100 to 140 Vdc for our example. In this scheme, the circuit includes truck-operated cell (TOC) contacts responsive to the position of the circuit breaker in the cell. These contacts are used to make the local control switch close contact (CS/C) operative only in the TEST position. The local control switch trip contact (CS/T) is operative in both the TEST and CONNECTED position. The TOC contacts are used to make the remote control contacts (201T and 201C) operative only in the CONNECTED position. Most users prefer that remote control contacts be operative only in the CONNECTED position. User preferences are less pronounced regarding local control circuits, with some users desiring that local circuits be operable only in the TEST position, and others desiring that local control circuits be operable in both CONNECTED and TEST positions.
- 3. The information provided in this document contains merely general descriptions or characteristics of performance which in case of actual use do not always apply as described or which may change as a result of further development of the products. An obligation to provide the respective characteristics shall only exist if expressly agreed in the terms of contract. All product designations may be trademarks or product names of Siemens AG or supplier companies whose use by third parties for their own purposes could violate the rights of the owners. Siemens Industry, Inc. 7000 Siemens Road Wendell, NC 27591 Subject to change without prior notice. Order No.: E50001-F710-A331-X-4A00 All rights reserved. © 2012 Siemens Industry, Inc. For more information, contact: +1 (800) 347-6659 www.usa.siemens.com/techtopics Symbols 52/a Aux switch (open when CB open) 52/b Aux switch (closed when CB open) 52SRC Close coil 52T Trip coil CS/C Control switch (local) close contact CS/T Control switch (local) trip contact RL Red indicating lamp GL Green indicating lamp 201C Interposing relay, close 201T Interposing relay, trip TOC/a Truck operated cell switch, closed when CB in connected position TOC/b Truck operated cell switch, open when CB in connected position LS Limit switch (spring charged)