GE Multilin 745

Auto-Configuration745
Transformer Management Relay
Setpoints
http://www.GEindustrial.com/multilin
5–6
GE Multilin
S2 SYSTEM SETUP !" WINDING 2 ! WINDING 2 NOM Φ-Φ VOLTAGE: “69.0 kV”
S2 SYSTEM SETUP !" WINDING 2 !" WINDING 2 RATED LOAD: “100 MVA”
S2 SYSTEM SETUP !" WINDING 2 !" WINDING 2 PHASE CT PRIMARY: “1500:1 A”
For a 3-winding transformer, the setpoints under
S2 SYSTEM SETUP/WINDING 3 must
also be set.
b) Onload Tap Changer
• Onload tap changer
• Variable voltage ratio
•CT
2
/ CT
1
= V
1
/ V
2
• Lower sensitivity on differential element
Solution:
• Tap position monitoring: V
2
= V
min
+ (n – 1)V
incr
For example, the onload tap changer changes the Winding 2 voltage, resulting in an
even greater CT mismatch. A perfectly matched Winding 2 CT ratio (based on the
tap changer position) is calculated as follows:
(EQ 5.2)
where n = current tap changer position
V
2(min)
= Winding 2 minimum voltage (at n = 1)
V
2(tap)
= Winding 2 voltage increment per tap
Thus, with the tap changer at position 33, the Winding 2 CT ratio must be 1428.6 /
1 to be perfectly matched. In this case, the mismatch factor is 1428.6 / 1500 =
0.952.
The 745 allows monitoring of the tap changer position via the tap position input.
With this input, the 745 dynamically adjusts the CT ratio mismatch factor based on
the actual transformer voltage ratio set by the tap changer.
Tap changers are operated by means of a motor drive unit mounted on the outside
of the transformer tank. The motor drive is placed in a protective housing containing
all devices necessary for operation, including a tap position indication circuit. This
indication circuit has a terminal for each tap with a fixed resistive increment per tap.
A cam from the drive shaft that provides local tap position indication also controls a
wiper terminal in the indication circuit, as illustrated below.
FIGURE 5–1: Tap Position Input
CT
2
(ideal) CT
1
V
1
V
2min()
V
2tap()
n 1–()+
---------------------------------------------------------------
×
500
1
-----------
220
61 0.5 n 1–()+
------------------------------------------
×==
ZERO
POSITION
TAP 1
TAP 2
TAP 3
TAP 4
TAP 6
TAP 7
TAP 8
TAP 9
etc.
WIPER
AT TAP 5
R
R
R
RR
R
R
R
R
ZERO POSITION
TERMINAL
(to TAP POSITION -)
WIPER
TERMINAL
(to TAP POSITION +)