- Email: [email protected]
Disconnecting Switches and Earthing Switches Theory Testing and Commissioning
Chapter 12
Disconnecting Switches and Earthing Switches Theory Testing and Commissioning 12.1 INTRODUCTION A disconnect switch (DS, also known as a disconnector or isolator switch) is a mechanical device used to isolate the equipment undergoing maintenance, such as a circuit breaker, in a safe manner. It can also be used to transfer the circuit bay from one busbar to another busbar, for example, in a bus coupler circuit in a substation. These devices can be provided with a safety earthing switch (ES) for the safety of the personnel who will work in the electric circuit within a substation or power station yards. Whilst a DS can carry load current, it can only disconnect or close the circuit in a no-load condition; there is an interlocking circuit in substations to prevent them from operation under load conditions. Mechanisms are normally installed to permit the operation of the DS by an operator standing at ground level. The operating mechanisms provide a swing arm or gearing to permit operation with reasonable effort by utility personnel. Motor operating mechanisms are also available and are applied when remote switching is necessary. The DS operation can be designed for vertical or horizontal operating of the switch blades. Several configurations are frequently used for switch applications, as seen in Figs. 12.1 12.7. These configurations include the following: G G G G G G G
Horizontally-upright mounted DS Vertically-mounted DS Double break switches V switches Hook-stick switches Pantograph switches Earthing switches
Practical Power System and Protective Relays Commissioning. DOI: https://doi.org/10.1016/B978-0-12-816858-5.00012-5 © 2019 Elsevier Inc. All rights reserved.
133
134
Practical Power System and Protective Relays Commissioning
FIGURE 12.1 Horizontally-upright mounted disconnect switch.
FIGURE 12.2 Vertically-mounted disconnect switch.
12.1.1 Load Break Switches A load break switch is a type of DS that can open or close on specified load currents. It is normally used to energize or de-energize a circuit that has some magnetic or capacitive currents as a transformer excitation current and high-voltage transmission cables with capacitive current.
Disconnecting Switches and Earthing Switches Chapter | 12
FIGURE 12.3 Double end break (double side break) disconnect switch.
FIGURE 12.4 Double end break V-disconnect switch.
135
136
Practical Power System and Protective Relays Commissioning
FIGURE 12.5 Hook-stick operated disconnect switch.
FIGURE 12.6 Pantograph disconnect switch.
12.1.2 High-Speed Earthing Switches High-speed ES are used to discharge the high voltage cables from the capacitive charging current. This current is very dangerous for the personnel working at the high-voltage cable end at a substation, paticularly if they are outdoors.
FIGURE 12.7 Earthing switch.
138
Practical Power System and Protective Relays Commissioning
12.2 DISCONNECT SWITCHES/EARTH (GROUNDING) SWITCHES TESTS This includes the following tests: 1. Mechanical check and function test including open/close and electrical and mechanical interlocks a. Check the horizontal level of the disconnecting switch in the open and close positions. b. Measure the distance between the axis of the two isolators of the disconnecting switch as per the drawings. c. Check that the mechanical indicator of the disconnecting switch is correct for the open and close positions. d. Check for the mechanical interlocks between the disconnecting switch and its ES. 2. Operating time test a. This test can be done using a stop watch. 3. Contact resistance test a. This test is done by micro-Ohm meter tester which injects 100 DC Amp and is connected as shown in Fig. 12.8.
FIGURE 12.8 Contact resistance measurement of the disconnecting switch.
Disconnecting Switches and Earthing Switches Chapter | 12
139
The results at site shown in Fig. 12.8 was in the range of 45 50 μΩ. 4. Insulation test a. This can be done by Megger tester at 5000 V DC. 5. High voltage AC test a. This test will be done during the first energization of the substation with a nominal voltage of the disconnecting switch.
Disconnecting Switches and Earthing Switches Theory Testing and Commissioning 12.1 INTRODUCTION A disconnect switch (DS, also known as a disconnector or isolator switch) is a mechanical device used to isolate the equipment undergoing maintenance, such as a circuit breaker, in a safe manner. It can also be used to transfer the circuit bay from one busbar to another busbar, for example, in a bus coupler circuit in a substation. These devices can be provided with a safety earthing switch (ES) for the safety of the personnel who will work in the electric circuit within a substation or power station yards. Whilst a DS can carry load current, it can only disconnect or close the circuit in a no-load condition; there is an interlocking circuit in substations to prevent them from operation under load conditions. Mechanisms are normally installed to permit the operation of the DS by an operator standing at ground level. The operating mechanisms provide a swing arm or gearing to permit operation with reasonable effort by utility personnel. Motor operating mechanisms are also available and are applied when remote switching is necessary. The DS operation can be designed for vertical or horizontal operating of the switch blades. Several configurations are frequently used for switch applications, as seen in Figs. 12.1 12.7. These configurations include the following: G G G G G G G
Horizontally-upright mounted DS Vertically-mounted DS Double break switches V switches Hook-stick switches Pantograph switches Earthing switches
Practical Power System and Protective Relays Commissioning. DOI: https://doi.org/10.1016/B978-0-12-816858-5.00012-5 © 2019 Elsevier Inc. All rights reserved.
133
134
Practical Power System and Protective Relays Commissioning
FIGURE 12.1 Horizontally-upright mounted disconnect switch.
FIGURE 12.2 Vertically-mounted disconnect switch.
12.1.1 Load Break Switches A load break switch is a type of DS that can open or close on specified load currents. It is normally used to energize or de-energize a circuit that has some magnetic or capacitive currents as a transformer excitation current and high-voltage transmission cables with capacitive current.
Disconnecting Switches and Earthing Switches Chapter | 12
FIGURE 12.3 Double end break (double side break) disconnect switch.
FIGURE 12.4 Double end break V-disconnect switch.
135
136
Practical Power System and Protective Relays Commissioning
FIGURE 12.5 Hook-stick operated disconnect switch.
FIGURE 12.6 Pantograph disconnect switch.
12.1.2 High-Speed Earthing Switches High-speed ES are used to discharge the high voltage cables from the capacitive charging current. This current is very dangerous for the personnel working at the high-voltage cable end at a substation, paticularly if they are outdoors.
FIGURE 12.7 Earthing switch.
138
Practical Power System and Protective Relays Commissioning
12.2 DISCONNECT SWITCHES/EARTH (GROUNDING) SWITCHES TESTS This includes the following tests: 1. Mechanical check and function test including open/close and electrical and mechanical interlocks a. Check the horizontal level of the disconnecting switch in the open and close positions. b. Measure the distance between the axis of the two isolators of the disconnecting switch as per the drawings. c. Check that the mechanical indicator of the disconnecting switch is correct for the open and close positions. d. Check for the mechanical interlocks between the disconnecting switch and its ES. 2. Operating time test a. This test can be done using a stop watch. 3. Contact resistance test a. This test is done by micro-Ohm meter tester which injects 100 DC Amp and is connected as shown in Fig. 12.8.
FIGURE 12.8 Contact resistance measurement of the disconnecting switch.
Disconnecting Switches and Earthing Switches Chapter | 12
139
The results at site shown in Fig. 12.8 was in the range of 45 50 μΩ. 4. Insulation test a. This can be done by Megger tester at 5000 V DC. 5. High voltage AC test a. This test will be done during the first energization of the substation with a nominal voltage of the disconnecting switch.