INO
OVERCURRENT RELAY
 
Application
 
Overcurrent relays type INO represent independent devices intended for selective protection of single-end supplied (radial) overhead and cable feeders, generators and transformers against overt oads and short circuits. For selective directional protection of both-end supplied feeders and of ring networks, a family of directional overcurrent reLays type INS is available.
 
Description
 
Overload protection
 
If the overload current exceeds the permissible value (continually adjustable in the range of 0,6 In to 1 ,8 In) for a time longer than set, upon expiry of the time set on the time delay scale, the final control relay will be activated, and a command for circuit breaker tripping will be released. The time delay settings are continually adjustable within 0,2 s and 6 s.
 
Short circuit protection
 

If the input current exceeds the value set on the scale for short circuit protection (adjustable within the range of 3 In to 10 In) the final control relay is practically immediately activated, and a command for circuit breaker tripping will be released. With the short circuit current in the range of 1,8 In to 3 In the overcurrent relay operation is identical to that of the overload protection.
Information on current magnitude is taken from current measuring transformers connected in appropriate phases of the protected equipment. Such information is processed in the measuring circuit, and in dependence of the position of potentiometer I> (in the range of 0,6 In to 1,8 In) and potentiometer I> (in the range of 3 In to 10 In) the comparators t> and I> can be activated, figs. 1 and 2.

Activation of comparator I> results in:

  • instantaneous activation of the auxiliary relay "b", the normally open contacts 12-13 of which are usually used to activate the automatic reclosing unit (APU) and the signall ing unit
  • activation of the auxiliary relay "a" after expiry of the time delay set on the scale t> in the range of 0.2 s to 6 s

If the overload current I> duration is shorter than the time set on scale t> , the relay "b" and the time delay member t> turn instantaneously back into their original state, and the time delay member will not activate the finals control relay "a".

Activation of comparator I>> results in an instantaneous activation of relays "a" and "b '. The scales I> , I>> and t> are Iogically arranged, easily accessible, clearly marked and graduated, with continual settings.
 
Features
 

With respect to the power supply method, two options of INO relays are available:with external power supply from an auxiliary source 110 V d.c. or 220 V d.c. and with internal power supply derived from the measuring current, thus no external source of power supply is required. When an external source of power supply is to be used, it is connected to terminals 10 and 11 of the unit (plus pole to the terminal 11) .The units are manufactured for the protection of one, two and three phases, and the same assemblies in the unit are then multiplied accordingly.
The devices for overcurrent protection are equipped with an instantaneous contact (terminals 12 and 13) which permits their operation in combination with the automatic reclosing unit (APU).
The overcurrent relays type INO are all solid state devices (static relays) what makes them highly reliable and accurate, with very good drout/pick-up ratio, low power requirements and practically unlimited life time.
Considering that the pick-up current is same for all phases, the overcurrent relays type INO are equipped with only three or only two scales continually adjustable:

  • a scale for overload current protection, I>
  • a scale for time delay setting, t> , and
  • a scale for short circuit current protection, I>>

When an INO unit is inserted for overcurrent protection in multiphase arrangements (the usual case), it will be activated as soon as current in any of the protected phases exceeds the selected current setting.
 
Denomination method
 

The INO type relays belong to the line of definite time overcurrent relays manufactured by Elko. In addition to the symbol INO every type of overcurrent relay has four additional symbols:

  1. number of protected phases
  2. equipped with I>> capability
  3. equipped with signalling
  4. options

The following symbols can occur on individual places:

Place I

  • 1-denotes that the overcurrent protection member is inserted into one phase
  • 2-denotes that the overcurrent protection member is inserted into two phases
  • 3-denotes that the overcurrent protection member is inserted into three phases

Place II

  • 0-denotes that the unit is not equipped with a short circuir protection member I>>
  • 4-denotes that the unit is equipped with a short circuit protection member I>>

Place III

  • 0-denotes that the unit is not equipped with phase fault signalling

Place IV

  • A-internal power supply
  • V-external power supply
  • C-the unit with external power supply, equipped with a separate final control relay for the member I>>, with the contacts wired to terminals 14 and 15

Example :
INO-340V -an overcurrent relay of INO type, with a definite time characteristic, for three phase protection, equipped with short circuit protection capability I>>, without phase fault signalling, external source of supply required.
 
Technical data
 
Rated current
5A, 1A
Setting range for overload current (I>)
0,6 In do 1,8 In
Setting range for short circuit current (I>>)
3 In do 10 In
Accuracy of current setting scales
5%
Setting range of time delay (t>)
0,2s do 6s
Accuracy of time setting scale
bolje od 50ms za t<1s 5% za t>1s
Drop out/pick-up ratio veæi od 0,9
Power drain :
-from the measuring path per phase at In = 5A

-from auxiliary supply source		 less than 10 VA (with internal power supply)
less than 2 V A (with external supply source)
at 110 V 4 W approx.
at 220 V 8 W approx.
Auxiliary voltage:
-from a storage battery or regulated power supply
-internal supply capability

Un = 110V= ili 220V=,
-10% +15%
only for In = 5 A
Contacts:
maximum voltage
maximum current
-continuous 10 A
-at make

250V

5A
10A
breaking capacity at cosj =1
for d .c. at L/ R = 40 ms
1000 VA

20W
Ambient temperature
-10oC do +50oC
Test voltage
2 kV, 50 Hz, 1 min.
Mass
2,6 kg
Dimensions
as in fig. 16
 
Data to be ordered
 
  • device type
  • rated current
  • auxiliary voltage rating (with the option V)