ABB KH-2 Instruction Leaflet

ABB
Effective: June 2008
Supersedes I.L. 41-138C, dated April 1995
( | ) Denotes Text Change since previous issue
( * ) Denotes Figure Change since previous issue
!
Before putting protective relays into ser-
vice, remove all blocking inserted for the
purpose of securing the parts during ship-
ment. Make sure that all moving parts
operate freely. Inspect the contacts to see
that they are clean and close properly, and
operate the relay to check the settings and
electrical connections.
1.0 APPLICATION
The type KH-2 instantaneous directional overcurrent
relay is used whenever a directional unit with an
adjustable pickup is desired.
A typical application is for directional lockout for cur-
rent balance paralleling when two or more load tap
changing transformers are connected in parallel. The
KH-2 will operate to allow only the proper control cir-
cuit (either the raise or lower control) to function
which will decrease the circulating current. The KH-2
is suitable since the normal voltage does not vary
more than 10% of rated value and the power factor
angle is between 60° and 90°.
For the type KH-2 relay with separate overcurrent
unit, proceed to the section of this instruction leaflet
describing this type.
All possible contingencies which may arise during installation, operation or maintenance, and all
details and variations of this equipment do not purport to be covered by these instructions. If further
information is desired by purchaser regarding this particular installation, operation or maintenance
of this equipment, the local ABB Inc. representative should be contacted.
CAUTION
Type KH-2
Instantaneous Directional
Overcurrent Relay
2.0 CONSTRUCTION and OPERATION
The type KH-2 consists of two cylinder directional
overcurrent units (D).
2.1. DIRECTIONAL OVERCURRENT UNIT (D)
The directional overcurrent unit is a product induction
cylinder type unit operating on the interaction
between the polarizing circuit flux and the operating
circuit flux.
Mechanically, the directional overcurrent unit is com-
posed of four basic components: A die-cast aluminum
frame, an electromagnet, a moving element assem-
bly, and a molded bridge.
The frame serves as the mounting structure for the
magnetic core. The magnetic core which houses the
lower pin bearing is secured to the frame by a locking
nut. The bearing can be replaced, if necessary, with-
out having to remove the magnetic core from the
frame.
The electromagnet has two series-connected polariz-
ing coils mounted diametrically opposite one another;
two series connected operating coils mounted dia-
metrically opposite one another; two magnetic adjust-
ing plugs; upper and lower adjusting plug clips, and
two locating pins. The locating pins are used to accu-
rately position the lower pin bearing, which is
threaded into the bridge. The electromagnet is
secured to the frame by four mounting screws.
The moving element assembly consists of a spiral
spring contact carrying member, and an aluminum
cylinder assembled to a molded hub which holds the
Instruction Leaflet
41-138D