ABB HU Instruction Leaflet page 2

To restraint Transf. 1
Figure 1. Type HU, HU-1 Relays - Front View Photo
Operating Ckt, Resistor (DU)
Harmonic Restraint Unit (DU)
Differential Unit (DU)
Parallel Reactor
(HRU Operate Filter)
TAP BLOCK
Restraint Transf. 1
Restraint Transf. 2
Restraint Transf. 3 (HU-1 only)
Restraint Transformers (DU)
Indicating Contactor Switch
(ICS)
Indicating Instantaneous Trip
(IIT)
To restraint Transf. 3 (HU-1 only)
To restraint Transf. 2
Figure 2. Type HU, HU-1 Relays - Rear View Photo
Parallel Filter-Reactor
(HRU Restraint)
Series Filter-Reactor
(HRU Restraint)
Operating Transformer
(HRU)
Operating Transf. (DU)
Refer to Figure 18
for component
location
HU-1 Only
Operating Circuit
Filter
Capacitor - 0.45 MFD
HRU Restraint Filter Circuit