Emco EE301-T, Manual

Page: 14 / 25

14
X
L
= the line reactance in ohms/phase.
R
L
= the line resistance in ohms/phase.
The LDC simulates the resistive & reactive drops across the line. The %R setting gives the
resistive drop which is in phase with line current. The polarity switch VR selects whether the
drop has to be added or subtracted from PT Voltage.
In +VR position this voltage is subtracted from the PT voltage so that its effect on AVR is to
Raise the voltage equal to the resistive drop to make the voltage at the load equal to nominal
value. In -VR position drop is added & its effect on AVR is to ‘LOWER’ the voltage. In normal
use, VR switch is kept on + posiiion.
The % X setting gives the reactive drop across the line. This drop is in phase quadrature to
the line current. The +VX gives lagging compensation and -VX gives leading compensation.
Since the reactive compensation is in quadrature, its effect on AVR magnitude is very less.
However, its effect is observable for power factors bet. 0.5 & 0.7 and is similar to VR compen-
sation i.e. +VX raises the voltage & -VX Lowers.the Voltage.
The PT I/P to the AVR is internally stepped down to 3.3V corresponding to 110V. The vector
sum of resistive & reactive drops i.e. LDC 0/P is added vectorially to the stepped down PT
voltage to get the sense voltage at load end.
TESTING OF LDC
a) Feed 110V PT to AVR and keep R = 108 & L = 112.
b) Keep %R & %X setting of LDC to minimum position.
c) Now the AVR is in dead-band condition. Feed 1A current through the terminals 5 & 6 on rear
panel.
d) Keep both polarity switches to +VR & +VX position.
e) Increase %R compensation from 0 to 20%, 'Raise’ indication should come.
f) Put polarity switch to -VR position, “Lower” indication should come.
g) Bring back %R control to zero position.
h) lncrease % X control from 0 to 20%, Raise indication should come. Put polarity Switch
to -Vx position, Lower indication should come.
(N.B.) - This can be observed only for a power factor of 0.5 to 0.7. For lower power factor
effect is not observable.
Note :- If above tests are not ok, then interchange CT connections at 5 & 6 and carry out
same tests.
CALIBRATION CHECK OF %R
a) Assuming current in phase with voltage (i.e. pf. = 1)
set L = 115V & R = 105V, %R = 0 & %X = 0.
Check operation of AVR without feeding 1Amp current to LDC.