horm4
TRANSCRIPT
Type HORM 4Pilot Wire Protection Relay
Type HORM 4Pilot Wire Protection Relay
HORM 4 relaywithdrawn from case
Features
l High speed operation.
l Equipped with supervision andinjection facilities.
l Pilot circuits upto 1000 ohms and1 microfarad.
l Upto four output contactsavailable.
Application
This is a well established type ofprotection for feeders. It is based onthe Merz-Price circulating currentsystem and suitable for operationover privately owned two core pilotswith a relatively high core resistance(upto 1000 ohms. loop) and lowintercore insulation level.
The majority of plain feeders can beprotected with this form ofprotection, which features a unitprotection scheme with no time orcurrent grading problems even onring circuits.
Relay description
The three line currents aresummated by a summationtransformer with a centre tap toprovide a single phase current forcomparison over a pilot circuit.A padding resistor is provided toadjust the pilot loop resistance to aconstant value of 1000 ohms, thusensuring that the settings remainclose to the design value for all pilotcircuits. The padding resistance isset to 0.5 (1000-Rp) on each relay,where Rp is the pilot loop resistancein ohms.
The operation of HORM4 relay canbe understood by referring toFigure 2 which shows the basiccircuit 2(c) and voltage distributionaround the pilots during one fullcycle of the current wave [2(a) and2(b)] during a through-fault/load.From Figure 2(c) it will be seen thatthe relay operating coil is basicallyconnected between the midpoint ofthe diodes D4/D5 and the centre-
tap of the summation CT secondarywinding. The relay can operatetherefore, only if the potential ofpoints a/b or c/d is positive withrespect to winding mid-points O� &O� respectively.
Figure 2(a) shows the voltagedistribution around the pilots duringthe positive half-cycle. It also showsthe components around the pilotloop circuit which are active duringthis half-cycle of current flow. It isobvious from the voltage diagramthat the potential of points a/b andc/d can either be zero or negative,but never positive. The samesituation results during negativehalf-cycle also (see Figure 2(b)).Stability is thus achieved duringthrough faults and load.
During internal faults, say, withinfeeds from both ends, diodes D4and D5 will allow the current fromeach half of the summationtransformer secondary to flowthrough the relay during alternatehalf cycles thereby causing fast relayoperation.
Pilot supervision
Reliability of the pilot wire protectiondepends greatly on the integrity ofpilots. It is therefore necessary tomonitor the healthiness of theinterconnecting pilots continuouslyand sound an alarm in case thepilots are found faulty. Pilot wiresupervision is usually carried out byinjecting a small dc current into thepilot circuit and monitoring itscontinuity of flow.
The pilot supervision circuits areshown in Figure1 itself. CapacitorsC1 are provided to block the dcsupervision current from flowingthrough the relay. A rectified accurrent of about 4.8 mA is injectedinto the pilots at one end throughthe injection transformer IT, rectifierRt resistor r1 and choke L. At theother end, a sensitive attractedarmature unit RL1 is connectedacross the pilots throgh resistor r1and diode d1 and choke L. Relay RL1normally remains picked-up underpilot healthy conditions. It drops-offonly when:
i) pilots are openedii) pilots are shortediii) pilots are cross-connected.
When RL1 drops off an alarm isgiven by the N/C contact of afollower relay RL2. RL2 is slugged ondrop off to allow for momentaryresetting of RL1 during heavythrough fault conditions which canreduce or neutralise the dcsupervision currents cyclically andcause RL1 to drop off intermittently.
Technical data
Current rating
1A/5A
Rated frequency
50 Hz
Current setting
l Receiving end:
Summation ratio 1/1/N
Type of fault Fault settings [%In]
N = 3 N = 5
A - N 25 18B - N 32 21C - N 42 25
For N = 3
Neutral connection in CT secondaryshould be made to terminal 9.
A � B 125B � C 125C � A 62A � B � C 72
For N = 5
Neutral connection should be madeto terminal 10.
l Sending end:upto 2 x receiving end.
Drop-off/pick-up value of relay
25% of setting
Aux. voltage relay &supervision
(a) 220, 110, 50/48, 30V dc(b) Injection: 240V ac 50 Hz.
Operating time
60 m.secs. at 3 x Is.
Throughfault stability
50 times relay rating
Accuracy
±10% of setting
Thermal rating
20 x rated current for 3 secs.
Pilot
Any type of pilot having aninsulation grade which canwithstand 500V between cores maybe used. The pilots should have aloop resistance excluding the relayof 1000 ohms. and a total intercorecapacitance of less than 1.0microfarad. The pilot circuit shouldbe capable of standing a pressuretest of 5 KV rms between the twocores connected together and earth.
CT requirements
Minimum knee point voltage of lineCTs
VK =n
50I
+ 1f (RCT + 2RL) volts
where
In = Rated current of relay (A)
If = Max through-fault currentunder steady stateconditions referred to theCT secy. circuit (A).
RCT = Resistance of line CT secy.winding (ohms)
RL = Resistance of a single leadfrom the line CTs to therelay (ohms).
The knee point voltage of a currenttransformer is expressed as thevoltage, applied to the secy. windingwith the primary on open circuit,which when increased by 10%causes the magnetising current toincrease by 50%.
It is not recommended that anyother burdens should be connectedin the same current transformercircuit but where this is unavoidablethe additional burdens should beadded into the above expression forknee point voltage. In addition tothe above, the secondarymagnetising current of the currenttransformers at opposite ends of thefeeder should not differ by morethan 0.05 In at
n
50I
volts.
Contacts
Four make contacts are provided onHORM 4. One normally closedcontact on supervision for pilotalarm.
Make and carry Make and carryCurrent continuously for 1 second Break
AC 1250VA with 7500VA with 1250VA withmaxima of 5A maxima of 30A maxima ofand 660V and 660V 5A and 660V
DC 1250W with 7500W with 100W (resistive)maxima of 5A maxima of 30A 50W (inductive)and 660V and 660V L/R = 0.04 second
with maxima of 5A & 660V
Contact rating
Figure 1:Typical schematic diagram of relay type HORM 4with pilot supervision
alarm
Figure 2:Behaviour of HORM 4 during external fault
D1�
Insulation
The relay will withstand 5 kV for1 second between the pilot andcase circuit and all otherindependent circuits. 2 kV rms for1 minute between all other caseterminals connected together andthe case.
2 kV rms for 1 minute betweenall other independent circuits ofthe relay including contactcircuits.
1 kV rms for 1 minute across thecontacts of the normally openoutgoing contact pairs.
Environmental withstand
The relay meets the requirementsof BS 2011 to clause 20/40/4and is satisfactory for normaluse.
Mechanical durability
The relay will perform aminimum of 10,000 operations.
Case size
1-1/2, D.E. � HORM 4
ID, S.E. - injection andsupervision
Information requiredwith order
Current rating 1A or 5A
PR:032:0799:A Printed in India.
ALSTOM Limited Pallavaram Works: 19/1, GST Road, Pallavaram, Chennai-600 043. India.Tel: 91-044-2368621 Fax: 91-044-2367276 Email: [email protected].
© 1998 ALSTOM Limited
Our policy is one of continuous development. Accordingly the design of our products may change at any time. Whilst every effort is made to produce up to date literature, this brochure shouldonly be regarded as a guide and is intended for information purposes only. Its contents do not constitute an offer for sale or advice on the application of any product referred to in it.
ALSTOM Limited cannot be held responsible for any reliance on any decision taken on its contents without specific advice