Functional Description

The Intelligent Electronic Device (IED) is designed for selective, reliable, and fast differential protection of busbars, T-connections, and meshed corners in up to six independent protection zones. It supports a wide range of substation configurations, including:

Single, double, and triple busbar arrangements

Configurations with or without transfer bus

Double-circuit breaker and one-and-a-half circuit breaker schemes

The IED is suitable for protecting medium-voltage (MV), high-voltage (HV), and extra-high-voltage (EHV) installations operating at 50 Hz or 60 Hz. It is capable of detecting all internal phase-to-phase and phase-to-earth faults in solidly earthed or low-impedance earthed systems, as well as all internal multi-phase faults in isolated or high-impedance earthed power systems.

Voltage Transformer (VT) Input Considerations

The inclusion of VT inputs in the IED enables a variety of voltage-related protection and monitoring functions, such as:

Under-voltage release

Residual over-voltage functions

Power functions

Metering

Voltage recording during faults

However, adding VT inputs reduces the number of available CT inputs. The device supports a maximum of 24 analogue inputs, shared between CT and VT channels. Therefore, ordering VT inputs will reduce the maximum number of CT inputs and consequently limit the size of the busbar arrangement that the IED can protect. In practice, the number of available CT inputs defines the maximum number of bays or feeders that can be supervised by the busbar protection scheme.

Current Transformer (CT) Requirements

The IED imposes very low requirements on the main current transformers, eliminating the need for interposing CTs. It fully supports the use of mixed CT secondary ratings (1 A and 5 A) within the same protection zone.

In typical applications, CTs with up to a 10:1 ratio difference can be used within one differential protection zone. Ratio matching and compensation are performed numerically through parameter settings within the IED, ensuring accurate and stable differential protection performance.