Alstom SHPM 101 - Section 6. TECHNICAL DATA; 6.18 Burdens and current transformer requirements; 6.19 Output contact ranges

SERVICE MANUAL R5888C
QUADRAMHO Chapter 2
Page 71 of 74
6.18 Burdens and current transformer requirements
Voltage burden less than 0.1VA, 0.4 lagging power factor per phase at 63.5V
phase to neutral.
Current burden per phase with balanced three phase rated current.
0.26VA (1A relay
Mho version
0.68VA (5A relay)
0.34VA (1A relay
Quadrilateral version
0.75VA (5A relay)
The current transformers should have a minimum knee point output voltage V
K
defined as:
V
K
= I
F
(1 + X/R) (R
B
+ R
CT
+ R
L
)
Where
I
F
= The maximum fault current at the relay Zone 1 reach point in
secondary terms.
X/R = Primary system ratio.
R
B
= Relay burden resistance.
R
CT
= CT internal resistance in secondary terms.
R
L
= Lead resistance from CTS to relay.
(lead and return for earth faults, lead only for phase faults).
The following table gives the values of relay burden resistance R
B
:
MHO or Lenticular Version
1A relay earth faults R
B
= 0.53Ω
1A relay phase faults R
B
= 0.26Ω
5A relay earth faults R
B
= 0.054Ω
5A relay phase faults R
B
= 0.027Ω
Quadrilateral Version
1A relay earth faults R
B
= 0.61Ω
1A relay phase faults R
B
= 0.34Ω
5A relay earth faults R
B
= 0.056Ω
5A relay phase faults R
B
= 0.03Ω
Where necessary ALSTOM T&D Protection & Control Ltd can supply details of
reduced CT requirements on some systems.
6.19 Output contact ranges
Make and carry for 0.2s 7500VA with maxima of 30A and 300V, ac or dc.
Carry continuously 5A ac or dc.
Break ac 1250VA
dc 50W resistive with maxima 5A, 300V
25W L/R = 0.04s