Page 198 - Practical Power System and Protective Relays Commissioning

Protection Relays Chapter | 18 199

Restricted earth fault protection;
Binary inputs for transformer mechanical protection, such as Buchholz
protection, safety value, winding and oil temperature protection, and
cooling fan system automatic operation;
Overfluxing (voltage/frequency ratio) protection.
The busbar protection IED includes the following functions and may
include more functions based on the system requirements:
High-impedance busbar differential protection or low-impedance biased
differential protection—it can be of the centralized or decentralized type;
Breaker failure (BF) protection;
Relay failure protection.

As we see above, we note that one IED can perform many protection
functions which were previously performed by a separate relay for each
function. This means more cost saving and more accuracy with the built-in
algorithm inside the IED.
Fig. 18.4.10 illustrates a protection IED relay.

FIGURE 18.4.10 Protection intelligent electronic device relay.

18.4.3.2 Control and Monitoring Intelligent Electronic Device

Control and monitoring of IEDs include the following functions and may
include more functions based on the system requirements:
Local control switching of CBs, isolators, and earthing switches;
Metering measurements including, P, Q, cos Φ, I and V, and F;
Event recording;
Circuit interlocking which in practice is done using hard wires and in
parallel software interlocking inside the IED;
Trip circuit supervision, but some utilities use a separate relay for this
function—an old electromechanical one;
SF 6 gas monitoring in GIS high-voltage system;
Event and sequence recording.