2. Type CDG 11
Overcurrent and Earthfault Relay
for AC Series Tripping
CDG 11 relay
withdrawn from case
Features
• Identical time/current
characteristics on all taps.
• High torque, ensuring consistent
timing even under adverse
conditions.
• No overshoot.
• Simple construction, easily
accessible.
• Dust tight drawout case and
tropicalised finish.
Application
Selective phase and earthfault
protection in time graded system for
AC machines, transformers, feeders
etc. These relays are used where dc
tripping supply is not available and
trip the circuit breakers directly using
the current from the current
transformers.
General description
The CDG series trip relay is a slightly
modified version of type CDG 11
relay which incorporates a secondary
winding on the electromagnet of the
CDG relay and an instantaneous unit.
When the disc unit operates and
closes its contacts, the instantaneous
element connected across the
secondary winding on the
electromagnet operates, and opens
its normally closed heavy duty
contacts to allow the fault current to
flow through the circuit breaker trip
coil. The relay will safely control ac
trip coil currents upto 150 amps.
at 150 volts. When the trip current/
voltage exceeds these values, an
external series resistor with or
without a shunt choke is required.
In all other respects, the ac series
tripping relay is identical to the
plain inverse time current relay
type CDG 11.
Technical data
The operating coil can be supplied
suitable for operation from
5.0 amps. or 1.0 amp. CT
secondaries and the following
standard setting ranges are
available.
50 - 200% adjustable in seven
equal steps of 25%
20 - 80% adjustable in seven equal
steps of 10%
10 - 40% adjustable in seven equal
steps of 5%.
Starting current
103 - 105% of current setting at
TMS 1.0.
Closing current
Not more than 130% current setting.
Resetting current
The disc will completely reset at 90%
or more of the current setting.
3. Time settings
Operating time
0-3.0 seconds or 0-1.3 seconds at
10 times the current setting.
Time/current characteristics are
identical to the IDMT characteristics
or CDG 11.
Resetting time
With the time multiplier set at 1.0,
the resetting time is 4 seconds and 9
seconds approximately for relays
having an operating time of 1.3
seconds and 3.0 seconds
respectively at ten times the current
setting.
Burdens
2VA at lowest tap
3.5VA at highest tap
Thermal rating
The maximum continuous current
ratings for 60°C rise in coil
temperature are as follows:
Frequency error
A frequency variation of 2 Hz. gives
timing errors of less than 8%.
The time grading of a protective
system would be unaffected by this
small error since all relays would
be similarly affected.
Temperature error
For an overload equal to ten times
the current setting, the percentage
timing errors at ambient
temperatures of +45°C and –5°C
are respectively
3.0 seconds relay : –3% and +4%
1.3 seconds relay : –4% and +4%
Instantaneous unit and
operation indicator
The instantaneous unit of the relay is
usually fitted with two pairs of hand
reset heavy duty ‘break’ contacts for
connecting externally across the trip
coils of the circuit breaker and
2 pairs of hand reset ‘make’
contacts for alarm indication
purpose. The instantaneous unit is
fitted with an operation indicator
which is hand reset by means of a
push-rod protruding through the
relay case.
Contact ratings
The two pairs of hand reset heavy
duty contacts in parallel can break a
maximum current of 150 amps. at
150 volts ac. The two additional
pairs of hand reset standard ‘make’
contacts when provided for alarm
purposes can make and carry for
0.5 second 7500VA with maximum
of 30 amps. and 660 volts, ac or dc.
Insulation
The relay will withstand 2.5 KV ac
r.m.s. 50Hz for one second between
all circuits and the case and
between all circuits not intended to
be connected together. It will also
withstand 1.25 KV ac r.m.s. 50Hz
for one second between mating
contacts in open position.
The relay will withstand 20 times
the maximum current setting for
3 seconds on any setting.
Accuracy
The relay conforms to error class
index E 7.5 as per BS 142-1966 and
7.5 as per IS 3231-1965, at ten
times reference current setting.
External and internal
circuit connections
Typical external and internal
connections for type CDG 31 three
phase overcurrent, alternatively
combined overcurrent and earthfault
protection, are shown in Figure 1.
Case and finish
Relays are supplied in drawout
cases suitable for flush or projection
mounting and are finished eggshell
black and tropicalised. The drawout
feature considerably simplifies
maintenance and permits testing to
be carried out easily and quickly.
The case is fitted with switches which
short circuit the associated current
transformers on withdrawal of the
relay unit from the case. A filter
breather is fitted which equalises
pressure inside and outside the case
without admitting dust.
Operating
coil tap
1
2
3
4
5
6
7
4.5
3.7
3.2
2.7
2.6
2.4
2.2
Times current
setting
4. Dimensions and weights
Maximum overall dimensions Approximate
Relay Case size Height Width Depth* gross weight
mm mm mm Kg.
CDG 11 1D Vert. 233 170 203 6.0
series trip
3D Hor. 233 454 203 15.5
3D Vert. 524 170 203 15.0
* Add 76 mm for maximum length of terminal studs, alternatively,
29 mm for terminal screws.
The approximate gross weights given above are inclusive of cartons,
mounting appendages and terminal details.
The relays comply fully with the requirements of IS 3231-1965 and are
suitable for use in normal tropical environments.
CDG 31
series trip
Single pole relays are mounted in
size 1D vertical case and triple pole
relays are mounted in size 3D
horizontal or vertical case, as
required.
Certified dimensional drawings of
case outlines, panel cut-outs and
mounting details are available on
request.
Information required with
order
1. Type of relay (CDG 11 or 31)
and system frequency.
2. Current setting range.
3. Characteristic (0 - 3.0 sec. or
0 - 1.3 sec. at 10 times current
settings).
4. Operation indicator inscription,
if required.
5. Case size.
6. Type of mounting - flush or
projection.
7. Current transformer ratio and
secondary winding resistance.
8. The knee-point voltage and the
maximum voltage obtainable
from the CT.
9. One way secondary lead
resistance from CT to relay.
10. Nominal current rating of the
trip coils.
11. The trip coil impedance with
`plunger down’ and with
`plunger up’ at the maximum
and minimum tripping currents.
12. The operating voltage and the
fault level of the primary circuit.
