1. & Transient Voltage Recovery Capacitors
Grading Capacitors
&
Transient Voltage Recovery
Capacitors

2. What Are Grading Capacitors
Type are high voltage capacitors installed on circuit breakers by two methods
Line to ground
Across multi-break contacts
They may be installed internally or externally

3. What Do They Do?
Grading Capacitors are used in combination with High Voltage Circuit Breakers with different purposes.
Single break Circuit Breakers:
Grading Capacitors can be used to increase the switching capacity of the breaker

4. Capacitors Connected Line-Gnd. Externally
Dead Tank
Capacitors Connected Line-Gnd. Externally
Breaker Contact
Capacitor
Ground Connection

5. Dead Tank
Capacitors Connected Line-Gnd. Internally

8. Multi-break Circuit Breakers
Installed across the contacts
Grading Capacitors ensure uniform voltage distribution across all contact points during normal and switching system operation 

9. Live Tank
Capacitors Connected Across Contats Internally

11. Capacitor Specifications
90 up to 300 kV
High customization range to match CB mechanical and electrical parameters
Sealed construction, maintenance free
High mechanical resistance to shock and vibration due CB‘s switching operation
Available in compliance with all international standards

12. Issues With Grading Capacitors
Background:
A number of disturbing incidents (violent failures, comprehensive leak problems, etc.) in recent years
Little qualitative knowledge concerning the stresses grading capacitors are subjected to in service exists
No international standards for testing grading capacitors are available

13. Leak is the most common problem type
Oil leaking out (both AIS and GIS)
SF6leaking in (in GIS)
Moisture ingress (in AIS)

26. Pre-Insertion Resistors
PIR is pre-insertion-resistor. This is a resistor of about ohms which gets temporarily closed before closing the circuit breaker. The sequence is (close order)->closing of PIR->10-12milliseconds->closing of main break.

27. But while opening, PIR is first disconnected by the Breaker operating mechanism and then i.e. after 10 ms, main contacts of Breaker are opened. The main purpose of PIR is to limit the initial charging current of line. As the charging current of long line will be much more, it is advisable to use Breaker having PIR in long transmission line.

29. When electrical circuit having capacitance or transformer which can have inrush. Also transformers may have large inrush current. Transmission line (due to its capacitance) is another such circuit.
For closing in such circuit first the PIR comes in circuit to limit the inrush current. When the main contacts close, the current through PIR becomes zero as the shunt path is bridged by main contact.