SZR

OVERCURRENT RELAY
 
Application
 

The overcurrent relay type SZR is an inverse time-delayed relay. It is intended for selective protection of single-end powered overhead and cable feeders, generators and transformer from overload and short circuits.

 
Opis
 
The information of current quantity in individual phases the relay reaches through current instrument transformers. If any of the three currents exeeds the magnitude of the current setting Ip, the comparator Ip > will be activated. The operation of the comparator will start the time delay element t = f (I) and this, after a certain time, depending upon current quantity, will cause the tripping relay to operate.
If the current reaches the magnitude of the short circuit current setting, the comparator I >> will cause an instantaneous operation of the tripping relay.
 
Relay contacts
tripping relay
signalling relay
Maximum voltage
250V
380 V
Continuous current
5A
5A
Current at make
10A
-
Breaking capacity at cosj = 1
1000VA
400VA
Breaking capacity for direct current
20W (pri L/R = 40 ms)
50W (ohmic load)

Test voltage
2 kV; 50 Hz, 1 min.
5 kV; 1,2/50 ms;; 0,5 J
1 kV; 1MHz; 400 imp/s; 2s across
2,5 kV; 1 Mhz; 400 inp/s; 2s along
 
Accuracy
 

Time delay characteistic

The error of time delay remains within 7,5% or 100 ms for any operating current and any current setting Ip.

Time coefficient TM

The error of time delay for any time coefficient TM remains within 7,5% or 100 ms with respect to the time measured at TM = 1, multiplied by the respective time coefficient.

Instantaneous Element I>>

The error of the instantaneous element I>> is also within 7,5% at any current setting Ip.
So, with respect to accuracy ratings, the relay SZR exceeds stronger requirements than those defined in BS 142: 1966, class E 7,5

Temperature Influence

Within the temperature range of -10°C to + 50°C the device remains within the specified ratings. Influence of Auxiliary Voltage

Influence of Auxiliary Voltage

Within changes of rated auxiliary voltage of !10% the change of time delay is within 1%.

Time of Thermal Stabilisation

1 hour under auxiliary voltage .

mass: 2,5 kg approx.
Dimensions: according to fig. 3.
 
Method of designation
 

The relays type SZR represent the family of inverse time-delayed relays. In addition to the type designation SZR, individual relay options recive other four symbols:

The symbols on individual places have the following meanings:

Place I

N - N -normal inverse curve
V -very inverse curve

Place II

K -in case, fig.3.

Place III

0 - earthfault (homopolar) protection
1 - single-phase protection
2 - two-phase protection
3 - three-phase protection Place IV

Place IV

0 - instantaneous element I>> is not existing
1 - instantaneous element I>> is existing

 
Characteristics
 

The SZR type relay is a static device (integrated circuits and discrete components) which offers high reliability, high accuracy, low power drain and long life. It also incorporates the feature of galvanic isolation of relay inputs and outputs from its internal circuitry, so that possible interference voltages from power circuits have been suppressed remarkably.
The device is equipped with a three-pole tripping relay, the contacts of which can be used for both tripping purpose and signalling of relay operation. The signalling of excess of current setting Ip (Ip>)and short circuit current setting (I >>) is available via the contacts of signalling relays.
 
SPECIFICATIONS
 
Rated current In
5A or 1A
Frequency
50Hz
Type of time delay to current interdependance
normal inverse curve
according to BS 142: 1966
very inverse curve
according to BS 142: 1966
Time coefficient TM settings
0,05; 0,1; 0,2; 0,3; 0,4; 0,5;
0,6; 0,7; 0,8; 0,9; 1;
Overload current Ip> settings
(0,5¸2) In, in steps
of 0,25 In each (phase)
(0,1¸0,4)In, in steps of
0,05 In each (homopolar)
Short circuit current I>> setting
K (1-4) Ip in steps of po 0,25 Ip
each (K=1 ili K=3);
or which means that I>> is blocked
Response time I>>
< 40 ms
Drop uot/pick up ratio
0,95 approx.
Overload
continuous
5 In
10s
15 In
30s
40 In
Relay response time

60 In
Power drain from the measuring circuit per phase
5%
Ip=0,5 In and I=2Ip (phase)
0,3 VA approx. for In=5A
0,2 V approx. for In=1A
Ip= 0,1 in and I=2p (homopolar)
0,2 VA approx. for In=5A
0,6 VA approx. for In=1A
Auxiliary voltage from the storage battery or regulated power supply
110V= or 220V=±10%
Power drain from the source of auxiliary supply voltage
5 approx. - relay contacts dropped-out
10W approx. - relay contacts picked-up for 110V=
9W approx. - relay contacts dropped-out
20 approx - relay contacts picked-up for 220V=
 
How to order
 
  • type of device
  • rated current
  • auxiliary voltage

For all inquiries please contact the manufacturer

Subject co change without prior notice.