Application

The high-impedance principle for busbar differential protection

provides a secure and dependable protection scheme against

faults within the measured zone. The high-impedance principle

has been used for many years for differential protection due to

the capability to manage through-faults also with heavy current

transformer (CT) saturation.

The relay’s high-impedance protection functions contain a

built-in blocking functionality, which is provided by the bus-wire

supervision functions to restrict faulty operations in case of

faults in the measurement circuits.

Additional standby (residual) earth-fault protection is provided

by the two non-directional earth-fault stages. The standby

earth-fault protection can be used together with the high

impedance protection functionality to protect motors,

generators and transformers against residual earth faults. The

measurements are taken from the earthing point of the protected object.

The residual earth-fault protection can also be used as bus-wire

supervision especially in new or retrofitting applications where

an earth-fault protection function is used for grounding the

measurement circuits where a short circuit or a break has

occurred. The grounding can be done by an external relay.