Auto-Transformer - ABB KD-10 Instruction Leaflet

41-490J
taps which terminate at the tap block (Figure 3,
page 36). They are marked:
Relay –
Ohms
0.2-4.5 0.23 0.307 0.383
0.75-21.2 0.87 1.16 1.45
1.27-36.6 1.5 2.0 2.5
Current flowing through the primary coil provides an
MMF which produces magnetic lines of flux in the
core.
A voltage is induced in the secondary which is pro-
portional to the primary tap and current magnitude.
This proportionality is established by the cross sec-
tional area of the laminated steel core, the length of
an air gap which is located in the center of the coil,
and the tightness of the laminations. All of these fac-
tors which influence the secondary voltage propor-
tionality have been precisely set at the factory. The
clamps which hold the laminations should not be dis-
turbed by either tightening or loosening the clamp
screws.
The secondary winding has a single tap which di-
vides the winding into two sections. One section is
connected subtractively in series with the relay ter-
minal voltage. Thus a voltage which is proportional
to the phase current is subtracted vectorially from
the relay terminal voltage. The second section is
connected to a potentiometer and a fixed loading re-
sistor and provides a means of adjusting the phase
angle relation between primary current and the in-
duced secondary voltage.
2.2

AUTO-TRANSFORMER

The auto-transformer has three taps on its main
winding, S, which are numbered 1, 2 and 3 on the
tap block. A tertiary winding M has four taps which
may be connected additively or subtractively to in-
versely modify the S setting by any value from -18 to
+18 percent in steps of 3 percent.
The sign of M is negative when the R lead is above
the L lead. M is positive when L is in a tap location
which is above the tap location of the R lead. The M
setting is determined by the sum of per unit values
between the R and L lead. The actual per unit values
which appear on the tap plate between taps are 0,
.03, .09 and .06.
2
Taps
0.537 0.690 0.920 1.23
2.03 2.9 4.06 5.8
3.51 5.0 7.02 10.0
Type KD-10 and KD-11 Compensator Distance Relay
The auto-transformer makes it possible to expand
the basic range of "T" ohms by a multiplier of
Therefore, any relay ohm setting can be made within
1.5 percent from the desired value by combining the
compensator taps T, T
to-transformer taps S and M, S
and M . See Tables I, II, and III for compilation of
C
settings available (page 13, page 14, & page 15).
2.3 TRIPPING UNIT
The device which acts to initiate tripping is a four-pole
cylinder unit which is connected open delta and oper-
ates as a three-phase induction motor. Contact-clos-
ing torque is produced by the unit when the voltage
applied to its terminals has a negative-phase se-
quence. Closing torque for the relay forces the mov-
ing contact to the left hand side as viewed from the
front of the relay. Contact-opening torque is pro-
duced when positive-phase sequence voltages are
applied. Hence, the cylinder unit has restraint or op-
erating torque as determined by the phase sequence
of the voltages applied to its terminals.
Mechanically, the cylinder unit is composed of three
basic components: a die-cast aluminum frame and
electromagnet, a moving element assembly, 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 spring
and snap ring. This is an adjustable core which has
a 0.020 inch flat on one side and is held in its adjust-
ed position by the clamping action of two com-
pressed springs. The bearing can be replaced, if
necessary, without having to remove the magnetic
core from the frame.
The electromagnet has two series-connected coils
mounted diametrically opposite one another to ex-
cite each set of poles. Locating pins on the electro-
magnet are used to accurately position the lower pin
bearing, which is mounted on the frame, with respect
to the upper pin bearing, which is threaded into the
bridge. The electromagnet is permanently secured
to the frame and cannot be separated from the
frame.
The moving element assembly consists of a spiral
spring, contact carrying member, and an aluminum
cylinder assembled to a molded hub which holds the
shaft. The hub to which the moving contact arm is
clamped has a wedge-and-cam construction, to pro-
vide low-bounce contact action. A casual inspection
S
------------- -
±
1 M
, and T with the au-
AB BC
and M , and S
A A
.
C