hager HR551 - Function; Residual Current Relays HR551; Correct Use; Functional Description

Function
Residual current relays HR551
5 Function
5.1 Residual current relays HR551
The device is a differential current protection and monitoring relay of type B, with one channel, config-
urable leakage pre-warning and an integrated Modbus RS-485 interface, which is compatible with the
type B-specific differential current transformers of the HR series.
5.1.1 Correct use
– Residual current monitoring
– Assembly on DIN rail according to IEC60715:2017
– Connection to external toroidal transformers (HR72x)
5.1.2 Functional description
The device enables continuous monitoring of rated fault currents in earthed power grids. The current
induced in the external transformer is detected in the device, measured and the effective value (TRMS)
is calculated.
5.1.3 Product characteristics
– Display to show parameters
– Three buttons for scrolling through the various screens and programming the device
– Digital output as pre-alarm function
– Digital input for external tripping
– RS-485 communication
5.2 Toroidal transformer HR72x
The HR72x series of devices are electronic differential current protection and monitoring transform-
ers of type B (IEC60755), which can be used together with HR551 and HR554 differential current pro-
tection and monitoring relays. Which device to choose depends on the maximum current of the moni-
tored circuit (In):
– HR721 for In: 80A
– HR722 for In: 160A
– HR723 for In: 250A
– HR724 for In: 400A
5.2.1 Correct use
– Assembly on DIN rail according to IEC60715:2017
– Assembly on mounting plate with clamp
– Connection to residual current relay (HR55x)
5.2.2 Functional description
The toroidal transformer transforms the measured current into a measurable quantity for the differen-
tial current relay.
Fehlerstromschutz-Relais 9