dth31
TRANSCRIPT
Type DTH 31, 32 DTTM 11, 12High Speed Biased Differential Relays
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Type DTH 31, 32 DTTM 11, 12High Speed Biased Differential Relays
DTH relaywithdrawn from case
Features
l High speed.
l Low burden.
l Immunity to magnetising inrush.
l Immunity to transients and surges
l Compact in size.
l Single pole version with separateflags for differential/highsetoperation available.
Application
DTH 31 and DTH 32 are triple polehigh speed biased differential relays� DTTM 11/DTTM 12 are singlepole versions of DTH 31/DTH 32respectively � designed to protectlarge power transformers, autotransformers and generatortransformers against internal faults.Biased to provide stability duringheavy through-faults, the relaysutilise second harmonic restraint toprevent operation by normalmagnetising in-rush currentsproduced when the transformer isenergised.
In addition, type DTH/DTTM relaysemploy fifth harmonic by-passcircuit to avoid possible mal-operation under over-excitedconditions.
An instantaneous highset circuitoverrides the biased differentialcircuit to clear heavy internal faultsin about one cycle.
Type DTH 31/DTTM 11 is applicablefor two-winding transformers andtype DTH 32/DTTM 12 for threewinding transformers.
Extremely low burdens are achievedby the use of input devices whichconvert current to voltage(transactors). Static circuitry isemployed throughout, and a singleattracted armature unit provides theoutput. These relays have theadvantage of small dimensions andincreased reliability over theirelectro-mechanical equivalents.Ideally, the CT primary rating shouldagree with the protected powertransformer�s full load rating, andwith the transformation ratio. This
ensures the secondary currentsflowing in the interconnecting pilotsare balanced and matched with therelay rating.
When interposing CTs are used forratio correction, the main CTsecondary should preferably be starconnected and the phase anglecorrection whenever necessaryshould be adopted on theinterposing CT by connecting themin star/delta.
DescriptionDTH 31
Figure 1 � block schematic diagram� shows a typical application with athree-phase two-windingtransformer.Input currents I2 and I1 from thepower transformer line CTs areadded vectorially in the centretapped restraint bias transactor T1.Three taps in each half of thetransactor primary enable biassettings of 15%, 30% and 45% to beobtained. The output of T1 is fullwave rectified and smoothed to
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obtain the restraint bias voltage levelVB. The centre tap of T1 is connectedto the differential circuit whichcomprises transactors T2, T3 andcurrent transformer T4 connected isseries. A tuned circuit which includesthe secondary of T2 is arranged toresonate at the second harmonicfrequency. The output of this circuit isrectified and smoothed to obtain theharmonic restraint voltage level VH.In addition, outputs of transactor T3
and current transformer T4 arerectified and smoothed to obtain thedifferential voltage VD and thehighset voltage level VO respectively.
The greater of the two restrainingvoltage levels VB and VH is detectedin one comparator and compared inmagnitude with the differentialoperating voltage level VD in asecond comparator stage. Whenthe operate voltage exceeds therestraining voltage by more than apreset amount, the secondcomparator produces an output tooperate the common relay drivecircuit. The highset voltage level VO
operates the relay drive circuit if thedifferential current exceeds ten timesthe rated current.
DTH 32
Figure 2 � block schematic diagram� shows an application with a three-phase three-winding transformer.Because current reversal is possible,the three inputs I1, I2, and I3 cannotbe added vectorially. Consequently,inputs to the DTH 32 are fed toseparate transactor/rectifier circuits,and the dc voltage outputs added toproduce a bias voltage VB. All othercircuitry is similar to that of the DTH31 relay.
The DTTM 11/DTTM 12 are similarin operation to DTH 31/DTH 32respectively.
Technical data
Current ratings
1A or 5A at 50 Hz.
Settings
Operate
The relay operates when differentialcurrent exceeds 15% relay ratedcurrent (fixed).
Bias
The bias setting is adjustable to15%, 30% or 45% by plugboardtaps.
Thermal ratings
The relay will withstand twice ratedcurrent continuously, 40 times ratedcurrent for 3 s and 100 times ratedcurrent for 1 s. Limiting value is170 times rated current. Thelimiting value must not be exceededand can be withstood for amaximum period of 0.25 s.
Operating time
The relay operating time fordifferential currents in excess oftwice rated current is typically about45 ms.
Harmonic restraint
Operation is prevented when thesecond harmonic content of thedifferential current exceeds 20%.
Burdens
DTH 31/DTTM 11
0.33VA per phase at rated current �1A relay.
1.0VA per phase at rated current �5A relay.
DTH 32/DTTM 12
0.39VA per phase at rated current �1A relay.
1.2VA per phase at rated current �5A relay.
Highset
DTH 31/DTH 32
The highset circuit operates whenthe differential current exceeds 10times the rated current.
DTTM 11/DTTM 12
8, 10, 12, 14, 16 x rated current(recommended setting 10 x ratedcurrent).
Contacts
Two pairs of normally open self resetcontacts rated to make and carry7500VA for 0.5 s, with maxima of30A and 660V.
Auxiliary supply
30, 110/125, 220/250V dc.Relays for use on 110/125 or
220/250V are supplied withsuitable external resistors.
CT requirements
Star connected and delta connectedcurrent transformers must have aknee-point voltage given by:
Vk = 40 I (RCT + 2 RL)
where Vk = Current transformerknee-point voltage(V).
I = Relay rated current(A).
RCT = Resistance of CTsecondary winding(Ohms).
RL = Resistance of eachpilot from the relay tothe CTs (Ohms).
Magnetising current
Less than 0.03 x I at Vk/4
Operation indicators
Independent flags for differentialand highset are provided on typesDTTM 11 and DTTM 12, commonflag indicator for DTH 31/DTH 32.
Insulation
The relay meets the requirements ofIS 3231/IEC 255-5 series C- 2 kVfor 1 minute.
Impulse voltage
The relay complies with therequirements of IS 8686/IEC255-4, Appendix E to class III.
High frequency interference
The relay complies with IS 8686/IEC255-22-1 Appendix C to class III.
Case
Relays are supplied in drawout casesuitable for flush mounting and arefinished eggshell black andtropicalised. The drawout featureconsiderably simplifies maintenanceand permits testing to be carried outeasily and quickly. A cradlemounted isolating switch isprovided which automaticallyisolates the trip circuit when thecradle assembly is withdrawn fromthe case for maintenance. Thisprevents any inadvertent tripping ofthe circuit breaker. The case is fitted
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* 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 and are suitable for use in normal tropical environments.
Dimensions and weights
Maximum overall dimensions Approximate
Relay Case size Height (mm) Width (mm) Depth (mm)* gross weight (Kg.)
DTH 31 3D Vert. 524 170 203 15
DTH 32 3D Hor. 233 454 203 16
DTTM 11 1½D Vert. 362 170 203 8.3
DTTM 12 1½D Vert. 362 170 203 8.3
Figure 2:Block schematic diagram of DTH 32
with CT shorting switches whichprevent open circuiting of the CTcircuits on withdrawal of the relayunit from the case. A filterbreather is fitted which equalisespressure inside and outside thecase without admitting dust.
DTH 31 and DTH 32 relays aremounted in 3D vertical and 3Dhorizontal cases respectively.
DTTM 11 and DTTM 12 relaysare mounted in 1½D verticalcases.
Information requiredwith order
1. Differential relay typeDTH 31/32DTTM 11/12
2. Relay current rating
3. Auxiliary voltage
PR:024:0799: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.