02/05/96 MIRI 01/96Ii

MIRIDigital Overcurrent& Earth Fault Relay

L1 L2 L3 E

I> I>> ON IE

RESET

0.5000

I> 0

0.550.10.20.40.8

x1x1

0000tI>

x10x1000.10.20.40.8

0000

0000

x10000t

x10x1000.10.20.40.8

0

00

tI>>

0.050.10.20.40.8h

DEFTDEFTDEFT50Hz

NINVVINVEINV60Hz

2.00

I>>

2.5124816

0.10

I 0E

0.20.20.40.8

x1

IE

MIRI-IE

PB

P&B EngineeringBelle Vue WorksBoundary StreetManchesterM12 5NG

Tel: 0161 230 6363Fax:0161 230 6464

E-mail mail@pbeng.co.uk

02/05/96 MIRI 01/96Iii

Contents

CONTENTS

1. INTRODUCTION....................................................................................................................................................12. APPLICATIONS.....................................................................................................................................................23. FEATURES AND CHARACTERISTICS ........................................................................................................................24. DESIGN ...............................................................................................................................................................3

4.1 Connections..................................................................................................................................................34.1.1 Analogue Inputs.........................................................................................................................................54.1.2 Output Relays - MIRI-IE............................................................................................................................54.1.3 Output Relays - MIRI-I ..............................................................................................................................54.1.4 Output Relays - MIRI-E .............................................................................................................................54.1.5 Output Relays - MIRI-ES ...........................................................................................................................54.2 Front Panels.................................................................................................................................................64.2.1 LED's.........................................................................................................................................................74.2.2 DIP Switches .............................................................................................................................................74.2.3 RESET Push button....................................................................................................................................74.3 Code Jumpers...............................................................................................................................................7

5 WORKING PRINCIPLES...........................................................................................................................................85.1 Analogue Circuits.........................................................................................................................................85.2 Digital Circuits.............................................................................................................................................85.3 Power Supply................................................................................................................................................85.4 Requirements for the main Current Transformers .........................................................................................8

6 OPERATION AND SETTINGS ...................................................................................................................................96.1 Layout of the Operating elements .................................................................................................................96.2 Setting of the Parameters by means of DIP Switches.....................................................................................96.2.1 Setting of the tripping characteristic for Phase Over current and Earth Fault ...........................................96.2.2 Setting of the Value of I> for the Phase Over Current Stage ....................................................................106.2.3 Setting of the Tripping Time (tI>) for the Phase Over Current Stage........................................................106.2.4 Setting of the Value (I>>) for the High Set Overcurrent Unit...................................................................116.2.5 Setting of the Tripping Time (tI>>) for the High Set Overcurrent Unit. ...................................................116.2.6 Setting of the Value (IE) for the Earth Fault Protection ...........................................................................116.2.7 Setting of the Tripping Time (tE) for the Earth Fault Protection ..............................................................126.2.8 Setting of the Nominal Frequency ............................................................................................................126.3 Indication of Faults ....................................................................................................................................126.4 Reset...........................................................................................................................................................126.4.1 Hand Reset by Pressing the <RESET> Push-button.................................................................................126.4.2 Reset by Each New Energization..............................................................................................................126.7 Setting value calculation ............................................................................................................................126.7.1 Low set stage ...........................................................................................................................................136.7.2 High set stage ..........................................................................................................................................136.7.3 Characteristic curve ................................................................................................................................136.7.4 Low set stage time multiplier/time delay ..................................................................................................136.7.5 High set stage time delay .........................................................................................................................13

7. RELAY CASE ......................................................................................................................................................147.1 Individual case ...........................................................................................................................................147.2 Rack mounting............................................................................................................................................147.3 Terminal connections..................................................................................................................................14

8. TEST AND MAINTENANCE ...................................................................................................................................149. TECHNICAL DATA MIRI - DIGITAL OVERCURRENT & EARTH FAULT RELAY ........................................................15

9.1 Measuring Inputs........................................................................................................................................159.2 Auxiliary Voltage........................................................................................................................................159.3 General Data..............................................................................................................................................159.4 Setting Ranges and Steps ............................................................................................................................15

02/05/96 MIRI 01/96Iiii

9.4.1 Definite Time Overcurrent Protection......................................................................................................159.4.2 IDMT Overcurrent Protection..................................................................................................................169.5. Inverse time characteristics .......................................................................................................................179.6 Output Relays .............................................................................................................................................189.7 System Data................................................................................................................................................189.8 Housing ......................................................................................................................................................199.9 Terminal Connection Details ......................................................................................................................20

10. ORDER FORM ..................................................................................................................................................21

02/05/96 MIRI 01/96I1

1. Introduction

The application of powerful microprocessors opens a new chapter for power system protectiverelaying. The digital processing of measured values and the ability to perform complex arithmetic andlogic operations, give digital protection relays significant performance and flexibility improvementsover their traditional analogue counterparts. Additional advantages - very small power consumption,adaptability, self-supervision, fault diagnosis through fault data recording, smaller physicalconstruction and selectable relay characteristics - all combine to allow the implementation ofaccurate and highly reliable protection schemes at a significantly reduced financial burden.

The development of microprocessor based protective relays and their introduction into the markethas been stimulated by the recent trend to replace analogue with digital equipment. This moderntrend has prompted the development of a new P&B protective relay family - the MI relay series.The superiority of digital protective relaying over traditional analogue devices, as embodied by theMI relay family, is summarised by the following features:

•• Integration of many protective functions in a single compact case•• High accuracy owing to digital processing•• Wide setting ranges with fine interim steps.•• User friendly setting procedure by means of DIP-switches.

The Digital Overcurrent and Earth Fault Relay, MIRI, is a universal protection device for mediumvoltage networks. Similarly for protection against undervoltage, overvoltage and neutral voltagedisplacement, the MIRV is available.

The MI relay family was designed as a low cost range of protection relays for application in mediumvoltage networks. Similar protection relays with extended functions, the MR series, are alsoavailable. They provide an additional alpha-numeric display for the indication of measured values andfaults as well as allowing data exchange via a serial interface and increased operational reliabilitythrough self-supervision. This comprehensive family of protection relays can satisfy the demands ofeven the most complex protection schemes:

MRI - Overcurrent Relay (Independent time/I.D.M.T + earth + directional facilities)MRI-V - Voltage Dependent Overcurrent RelayMREF - Restricted Earth Fault RelayMRAR - Auto-Reclosing RelayMRMF - Mains Failure RelayMRVT - Voltage ProtectionMRFT - Frequency ProtectionMROS - Vector Surge or Rate of Change of FrequencyMRNS - Negative Sequence RelayMRRP - Power RelayMRCS - Check Synchronising RelayMRFF - Field Failure RelayMRDG - Differential Relay

To complement the MI & MR series, a range of Auxiliary, Timing and Tripping devices are alsoavailable.

02/05/96 MIRI 01/96I2

2. Applications

The Digital Overcurrent and Earth Fault Relay, the MIRI, is a universal protection device formedium voltage networks. The protective functions of the MIRI are summarised as follows:

• Selectable protective functions between :- Definite time overcurrent relay- Inverse time overcurrent relay

• Inverse definite minimum time (IDMT) overcurrent relay with the followingselectable characteristics in accordance with BS 142 and IEC 255-4:

- Normal Inverse- Very Inverse- Extremely Inverse

• An independent stage for the fast tripping of short circuit protection.• Two-stage overcurrent time protection for phase current.• Overcurrent time protection for earth fault current.

Furthermore, the MIRI relay can be employed as back-up protection for distance and differentialprotective relays.

3. Features and characteristics

• Complete digital processing of the sampled measured values• Digital filtering of measured values using discrete fourier analysis to suppress high

frequency harmonics and d.c component induced by faults or system operations• Wide setting ranges with fine setting steps• Outstanding design flexibility for easy selection of appropriate operational scheme

for numerous applications• Wide voltage range for DC or AC power supply• Withdrawable modules with automatic short circuit of C.T. inputs

02/05/96 MIRI 01/96I3

4. Design4.1 Connections

Application Diagram

POWER

SUPPLY

1 2 CASE

Supply

MIRI-IE

Typical Earthing Shown

TRIP SIGNAL7

5

3

6

48

13

11

9

12

1014

1519

17I E

I>

21

22

23

24

25

26

27

28

L1

L2

L3

I1

I2

I3

IE

S2P2

P1

S1

TRIP SIGNALI>>

Application Diagram

POWER

SUPPLY

1 2 CASE

Supply

MIRI-ITypical Earthing Shown

TRIP SIGNAL7

5

3

6

48

13

11

9

12

1014

I>

21

22

23

24

25

26

L1

L2

L3

I1

I2

I3

S2P2

P1

S1

TRIP SIGNALI>>

02/05/96 MIRI 01/96I4

Application Diagram

POWER

SUPPLY

1 2 CASE

Supply

MIRI-ETypical Earthing Shown

TRIP SIGNAL7

5

3

6

48

13

11

9

12

1014

I

E>

27

28

L1

L2

L3

IE

TRIP SIGNALE>>

I

CBCT 27

Application Diagram

POWER

SUPPLY

1 2 CASE

Supply

MIRI-ESTypical Earthing Shown

TRIP SIGNAL7

5

3

6

48

27

28

L1

L2

L3

IE

CBCT 27

02/05/96 MIRI 01/96I5

In the following; the functional description refers to the MIRI-IE. With a few exceptions; no earthfault detection for the MIRI-I and no phase measurement for the MIRI-E and MIRI-ES; allfunctions are valid for the other units.

4.1.1 Analogue Inputs

The constantly monitored measuring values are galvanically decoupled, filtered and finally fed to theanalogue/digital converter. The protection unit receives these analogue input signals of the phasecurrents I1, I2, I3 and residual current IE, each via separate input transformers.

4.1.2 Output Relays - MIRI-IE

The MIRI-IE is equipped with one tripping relay for low set overcurrent, one for high setovercurrent protection and one for earth fault protection.

•• Tripping I>•• Tripping I>>•• Tripping IE

4.1.3 Output Relays - MIRI-I

The MIRI-I is equipped with one tripping relay for low set overcurrent and one for high setovercurrent protection.

• Tripping I>• Tripping I>>

4.1.4 Output Relays - MIRI-E

The MIRI-E is equipped with one tripping relay for low set earth fault and one for high set earthfault protection.

• Tripping IE>• Tripping IE>>

4.1.5 Output Relays - MIRI-ES

The MIRI-ES is equipped with one tripping relay for earth fault protection.

• Tripping IE

02/05/96 MIRI 01/96I6

4.2 Front Panels

L1 L2 L3 E

I> I>> ON IE

RESET

0.5000

I> 0

0.550.10.20.40.8

x1x1

0000tI>

x10x1000.10.20.40.8

0000

0000

x10000t

x10x1000.10.20.40.8

0

00

tI>>

0.050.10.20.40.8h

DEFTDEFTDEFT50Hz

NINVVINVEINV60Hz

2.00

I>>

2.5124816

0.10

I 0E

0.20.20.40.8

x1

IE

MIRI-IE

PB

L1 L2 L3 E

I> I>> ON I E

RESET

0.05000

I> 0

0.10.20.20.40.8

x1x1

0000tI>

x10x1000.10.20.40.8

0000

0000

00

tI>>

0.050.10.20.40.8h

DEFTDEFTDEFT50Hz

NINVVINVEINV60Hz

0.050

I>>

0.55124816

MIRI-I

PB

RESET

0.1000

I>

0.20.20.40.8

x1x1

0000tI>

x10x1000.10.20.40.8

0000

0000

00

tI>>

0.050.10.20.40.8

DEFTDEFTDEFT50Hz

NINVVINVEINV60Hz

0.50

I

1124816E>>

MIRI-E

I> I>> ON

PB

RESET

00

x1x1

00

x1x1

00

tI>>

0.10.20.40.8x10

0.20

I

0.250.10.20.4x5x25

MIRI-ES

ONIE

x100

E>>

PB

02/05/96 MIRI 01/96I7

The front panel of the MIRI-IE relay comprises the following operation and indication elements;

• 7 DIP switches for the setting of the tripping values and times.• 8 LED's for fault indication.• 1 Push button for RESET.

4.2.1 LED's

On the front panel there are 8 LED's, their functions are indicated by the appropriate indicationsabove them. LED "ON" indicates the readiness for service, the other 7 LED's are used for faultdisplay and indicate the of type of fault and the respective phase.

4.2.2 DIP Switches

The 7 sets of DIP switches on the front plate serve to adjust the tripping values, times,characteristics and mains frequency.

NOTE: Please note that during Definite Time operation the associated time delay dip switchesare used to set the time delay before tripping. When the unit is in NINV, VINV or EINV then theassociated dip switches act as Times Multiplications Settings as shown on the appropriate curve

4.2.3 RESET Push button

The RESET push button is used to acknowledge faults and reset after fault clearance.

4.3 Code Jumpers

Behind the front panel of the MIRI-ES are two code jumpers used to pre-set the followingfunctions:

Position Jumper 1 Jumper 2OFF LED: Manual Reset Trip Relay: Manual ResetON LED: Auto Reset Trip Relay: Auto Reset

Note: LED and/or Trip Relay can only be reset via RESET push-button when jumpers in position "OFF".

The following figure shows the position and designation of the code jumpers

J1 J2

Code Jumper ON

Code Jumper OFF

Front Board

Code Jumper

02/05/96 MIRI 01/96I8

5 Working Principles

5.1 Analogue Circuits

The incoming currents from the external current transformers are converted to internal signals inproportion to the currents, via the internal input transducers and shunt resistors. The noise signalscaused by inductive and capacitive coupling are suppressed by an analogue RC filter circuit. Theanalogue signals are fed to the A/D converter of the micro-processor and transformed to digitalsignals through sample-hold circuits. All further processing is carried out on these digitised values.The analogue signals are sampled with a sampling frequency of 800 Hz, namely a sampling rate of1.25 mS for every measured quantity.

In order to achieve a sensitive earth current measurement, an operational amplifier is connected tothe earth current input circuit before the analogue signal enters the A/D converter.

5.2 Digital Circuits

The essential component of the MIRI relay is a powerful micro-controller. All of the operations,from the analogue digital conversion to the relay trip decision, are carried out by the micro-controllerdigitally. The relay program, located in EPROM, allows the CPU of the micro-controller to calculatethe three phase currents and earth fault current in order to detect a possible fault.

For the calculation of the current value, an efficient digital filter, based on the Fourier Analysis(DFFT - Discrete Fast Fourier Transformation), is applied to suppress high frequency harmonics andDC components caused by fault induced transients or other system disturbances. The actualcalculated current values are compared with the relay settings. When a current exceeds the startingvalue the unit starts the corresponding time delay calculation. When the set time delay has elapsed, atrip signal is given.

5.3 Power Supply

Vaux = 24V in a range from 16V to 60V ACor in a range from 16V to 80V DC

Vaux = 110V in a range from 50V to 270V ACor in a range from 70V to 360V DC

5.4 Requirements for the main Current Transformers

In order to ensure the correct operation of the MIRI range of relays, protection class CT's must beutilised. Instrument CT's are NOT a suitable alternative.

CT's should be chosen such that saturation, or loss of accuracy does not occur within the settingsand operation ranges of the relays. In the absence of known settings the following may be regardedas an approximate guide.

For 1A secondary

CT class 5P20 or 10P20 2.5VA (Allowing for up to 1Ω of secondary lead resistance)

For 5A secondary

CT class 5P20 or 10P20 5VA (Allowing for up to 0.5Ω of secondary lead resistance)

with due regard to a suitable CT ratio and fault level capacity.

02/05/96 MIRI 01/96I9

6 Operation and Settings

6.1 Layout of the Operating elements

All DIP switches required for the setting of parameters are located on the front panel, see figuresshowing front panel.

6.2 Setting of the Parameters by means of DIP Switches

For better comprehension of the DIP switches in this chapter the following are accepted:

1.

DIP Switch is turned off (OFF Position)

DIP Switch is turned on (ON Position)

2. Unlike the DIP switches shown on the front panel of the MIRI, the examples given are numberedand the ON position is marked.

6.2.1 Setting of the tripping characteristic for Phase Over current and Earth Fault

The following tripping characteristics can be adjusted:

1. Definite Time Tripping Curve - DEFT (Definite)

2. IDMT Tripping Curves - NINV (Normal Inverse)- VINV (Very Inverse)- EINV (Extremely Inverse)

By setting DIP switch 1,2 or 3 of the switch set shown below to the ON position, it is possible toselect one of the three IDMT tripping curves. If Definite Time is required, all three of the DIPswitches must be set to the DEFT position. In the case of an invalid setting for the DIP switches, forexample, if several switches are simultaneously set to the ON position, a Definite Time trippingcharacteristic with the smallest possible tripping time is automatically selected. This ensures that theprotected device cannot be overloaded under any circumstances. Setting ranges and characteristicsare detailed in Chapter 9.

1

2

3

4

ON

NINV

VINV

EINV

60Hz

DEFT

DEFT

DEFT

50Hz

Please Note: The MIRI-IE relay provides identical tripping characteristics for bothovercurrent and earth fault inputs.

02/05/96 MIRI 01/96I10

6.2.2 Setting of the Value of I> for the Phase Over Current Stage

With the aid of DIP Switch group I>, it is possible to adjust the response value for phase overcurrent tripping in the range 0.5 - 2.05 x In. The tripping value is calculated from the sum of theindividual settings of all the DIP switches.

Example

A tripping value of 1.0 x In is required, therefore switches 2 and 4 are switched on.

1

2

3

4

ON

0.55

0.1

0.2

0.4

0.5

0

5

6

0.8

RESERVED

0

0

0

I> DIP Switches

The response value for the phase

over current is then calculated as

follows:

I> = 0.5 + 0.1 + 0.4 = 1.0 x In

6.2.3 Setting of the Tripping Time (tI>) for the Phase Over Current Stage

With the aid of the DIP Switch group tI>, it is possible to select the tripping time for the phase overcurrent in the range 0.1 - 150 s. There are four switches available to adjust the set value (switches 3to 6) and two switches to select the multiplication factor (switches 1 and 2). The set value iscalculated from the sum of the individual factors (switches 3 to 6) multiplied by the set multiplicationfactor, x1, x10 or x100 are possible. If switches 1 and 2 are both set to ON, then the setting is invalidand gives an automatic multiplication factor of 1. If all the switches from 3 to 6 are set to the OFFposition, then the tripping time is equal to the relay operating time, approximately 30 mS.

Example

A tripping time of 10s is required, therefore switches 1, 4 and 6 are switched on,

1

2

3

4

ON

x10

x100

0.2

0.4

x1

0

5

6 0.8

0

0

0

tI> DIP Switches

The tripping time is then

calculated as follows:

tI> =( 0.2 + 0.8) x 10 = 10s

x1

0.1

Note: The multiplication factor must be set to 1 for IDMT tripping characteristics, then the set valuecorresponds to the time factor tI> (See IDMT characteristic curves, Chapter 9.5).

02/05/96 MIRI 01/96I11

6.2.4 Setting of the Value (I>>) for the High Set Overcurrent Unit.

With the aid of DIP Switch group I>> it is possible to adjust the value for the high set overcurrentunit in the range of 2.0 - 33.5 x In. The tripping value is calculated as described in 6.2.2.

Example

A value of 8.0 x In is required, therefore switches 3 and 4 are switched on.

1

2

3

4

ON

2.5

1

4

8

2.0

0

5

6 16

0

0

0

I>> DIP Switches

The High Set Overcurrent

value is then calculated

I>> =2 + 2 + 4 = 8.0 x In2

0as follows:

6.2.5 Setting of the Tripping Time (tI>>) for the High Set Overcurrent Unit.

With the aid of the DIP Switch group tI>>, it is possible to adjust the tripping period for the High SetOvercurrent unit in the range of 0.05 - 1.55s. The setting time is calculated from the sum of theindividual factors of all the DIP switches set to on. If all the switches are set to off, then the trippingtime is equal to the relay operating time, approximately 30mS.

Example

A tripping time of 0.5s is required, therefore switches 2 and 4 are switched on,

1

2

3

4

ON

0.05

0.1

0.4

0.8

0

0

5

6

0

0

0

I>> DIP Switches

TheTripping Time is then

calculated as follows:

I>> =0.1 + 0.4 = 0.5s0.2

0

t

If switch 6 is set to ∞, the High Set Overcurrent is inhibited, irrespective of other switch settings.

6.2.6 Setting of the Value (IE) for the Earth Fault Protection

The setting procedure is identical to that described in paragraph 6.2.2.

02/05/96 MIRI 01/96I12

6.2.7 Setting of the Tripping Time (tE) for the Earth Fault Protection

The setting procedure is identical to that described in paragraph 6.2.3.

6.2.8 Setting of the Nominal Frequency

For correct digital filtering, the applied FFT-Algorithm used for the data calculation, requires thenominal frequency of the system to be protected. The nominal frequency can be selected to 50 or60Hz by means of DIP switches on the front panel.

6.3 Indication of Faults

For fault indication the MIRI provides 7 LED's with the following functions:

LED L1 - Fault in Phase L1LED L2 - Fault in Phase L2LED L3 - Fault in Phase L3LED E - Earth FaultLED I> - Serves to indicate tripping from a phase overcurrentLED I>> - Serves to indicate tripping from a phase short circuitLED IE - Serves to indicate tripping from a Earth Fault

Example

In the case of a 2 phase short circuit between L1 and L2, then LED's L1, L2 and I>> would light up.

If a relay was energised because of a fault but the fault current had fallen below the tripping levelbefore tripping could occur, then this is stored and indicated by a slowly flashing LED correspondingto the fault indicated. This indication can be reset with the <RESET> push-button.

6.4 Reset

6.4.1 Hand Reset by Pressing the <RESET> Push-button

When the <RESET> push-button is pressed, the output relays immediately reset and all LED's areextinguished.

6.4.2 Reset by Each New Energization

At each new energization of the unit, the unit self resets and the LED's indicate any faults occurringat that time.

6.7 Setting value calculation

In order to ensure that protection relays form an integral part of any system, a full protection co-ordination study should normally be undertaken which considers both upstream and downstreamequipment. Further details may be obtained by contacting P&B Engineering.

In the absence of a suitable study, the following provides a brief guide;

02/05/96 MIRI 01/96I13

6.7.1 Low set stage

For plain and transformer feeders, the low set stage pickup is normally taken as 120% of anydownstream protection and 80% any upstream protection

In the absence of upstream and downstream protection setting information, a setting of 150% of thefull load current is normally used for transformer feeders.

6.7.2 High set stage

For plain feeders, this is not normally used. However, when used it is normally taken as 120% and80% of any downstream and upstream high set protection respectively.

For transformer feeders, this is normally set to 120% of the actual through fault level for secondaryfaults.

6.7.3 Characteristic curve

This is normally selected to suit both the upstream and downstream protection characteristic toachieve the minimum of crossover.

6.7.4 Low set stage time multiplier/time delay

This is normally selected to give sufficient time delay between upstream and downstream operatingtimes to allow for breaker clearance and measurement errors etc. This is usually taken as 0.3 - 0.4seconds

6.7.5 High set stage time delay

This is normally set at the minimum possible, or as 6.7.4.

02/05/96 MIRI 01/96I14

7. Relay case

The MIRI is delivered in an individual case for flush mounting.

7.1 Individual case

The MIRI is supplied in a UK manufactured industry standard drawout case suitable for flushmounting. For case dimension and cut-out, refer to Technical Data.

7.2 Rack mounting

MIRI relays may be supplied mounted in 19" racks if specified by the user.

7.3 Terminal connections

The MIRI plug in module is supplied in a case which has a very compact plug and socket connector.The current terminals are equipped with self closing short circuit contacts. Thus the MIRI modulecan be unplugged even with current flowing without endangering personnel.

8. Test and maintenance

Currents may be supplied to the input transformers to test the behaviour of the relay. By switchingon test currents and measuring the tripping time, the whole system can be accurately tested. Aportable test case can be supplied which is suitable for testing the MIRI .

All measuring input circuits of the MIRI are of static design and the relay functions are fullydigitised. Thus, the MIRI has no particular demand on maintenance.

02/05/96 MIRI 01/96I15

9. Technical Data MIRI - Digital Overcurrent & Earth Fault Relay

9.1 Measuring InputsRated Current, In 1A or 5ARated Frequency, Fn 50/60Hz

Power Consumption @ In = 1A 0.2VA @ In = 5A 0.1VA

Thermal Withstand, Half-wave 250 x In for 1s 100 x In for 10s 30 x In Continuously 4 x In

9.2 Auxiliary VoltageVaux = 24V in a range from 16V to 60V AC

or in a range from 16V to 80V DCVaux = 110V in a range from 50V to 270V AC

or in a range from 70V to 360V DC

Power Consumption @ 24V 3W quiescent, 6W operating @ 110V 3W quiescent, 6W operating

9.3 General DataDrop Out Ratio >97%Drop Out Time 30mSTime Lag Error ± 10mSMinimum Operating Time 30mSTransient Over-reach ≤ 5%

9.4 Setting Ranges and Steps9.4.1 Definite Time Overcurrent Protection

Setting Range Step TolerancesI> Is

tI>0.5 - 2.05 x Inx1: 0.1 - 1.5sx10: 1.0 - 15sx100: 10 - 150s

0.05 x In0.1s1.0s10s

±5%±3% or ±10mS±3% or ±10mS±3% or ±10mS

I>> ItI>>

2.0 - 33.5 x In0.05 - 1.55s

0.5 x In0.05s

±5%±3% or ±10mS

IE IstIE

0.1 - 1.6 x Inx1: 0.1 - 1.5sx10: 1.0 - 15sx100: 10 - 150s

0.1 x In0.1s1.0s10s

±5%±3% or ±10mS±3% or ±10mS±3% or ±10mS

MIRI-ESIEDefinate TimeOnly

IE>

tIE

0.002 -0.00950.01 - 0.04750.05 - 0.2375

INST - 1.4s1 - 14s

0.00050.00250.01250.1s1s

02/05/96 MIRI 01/96I16

9.4.2 IDMT Overcurrent Protection

Tripping characteristics in accordance with IEC 255-4 or BS 142

Normal Inverse t = 0.14 tI> [s]

(I/Is)0.02 - 1

Very Inverse t = 13.5 tI> [s] (I/Is) - 1

Extremely Inverse t = 80 tI> [s]

(I/Is)2 - 1

Where t = Tripping TimetI> = Time MultiplierI = Fault CurrentIs = Setting Value of the Current

Setting Range Step TolerancesI> Is

tI>0.5 - 2.05 x In0.1 - 1.5s

0.05 x In0.1

±5%±5% for NINV andVINV±7.5% for EINV at10 x Is

I>> ItI>>

2.0 - 33.5 x In0.05 - 1.55s

0.5 x In0.05s

±5%±3% or ±10mS

IE IstIE

0.1 - 1.6 x In0.1 - 1.5s

0.1 x In0.1s

±5%±5% for NINV andVINV±7.5% for EINV at10 x Is

IE>>

MIRI-E ONLY

IE>>

tIE>>

0.5 - 16 x In

0.05 - 1.55s

0.05 x In

0.55

02/05/96 MIRI 01/96I17

9.5. Inverse time characteristics

Normal Inverse Extremely Inverse

Very Inverse Definite Time

I/I s

02/05/96 MIRI 01/96I18

9.6 Output Relays

Number of Relays 3Contacts 2 Change-over for each Trip Relay I> and I>>

1 Change-over for Trip Relay IE

Breaking Capacity 1250VA @ AC, 150W @ DCResistive 380V AC, 125V DCMaximum Current 5AMaking Current (16mS) 20A

9.7 System Data

Design Standard IEC 255-4, BS 142

Temperature Range -40°C to +85°C (Storage)-20°C to +70°C (Operation)

Environmental Protection 95% Humidity @ 40°C for 56 Daysas per DIN IEC 68 Part 2-3

Test Voltages as per EN50081-1, EN50082-2

Insulation Test 2.5kV / 50Hz / 1 min.

Impulse Test 5kV, 1.2 / 50mS, 0.5J

High Frequency Interference Test 2.5kV / 1MHz

Burst Transient Test 4kV / 2.5KHz, 15mS

ESD Test 8kV

RFI Suppression Test 10V/m, 27 - 500MHz, 1 Octave/3 min.

EMI Suppression Test 10V/m

Mechanical Tests

Shock IEC 41B (CO) 38, Class 1Vibration IEC 41B (CO) 35, Class 1

Degree of Protection IP52 (Front)IP00 (Rear)

Weight Approx. 2Kg.

02/05/96 MIRI 01/96I19

9.8 Housing

Throughout the MI series range a modular housing system has been employed, utilising the latesthigh quality UK manufactured industry standard case components. This approach affords maximumflexibility for both the relay scheme designer and the maintenance engineer. The relay modules arefully withdrawable for ease of maintenance and where applicable incorporate automatic short-circuiting CT connections to avoid dangerous open circuit CT overvoltages. A clear plasticremovable front cover is provided for inspection purposes.

MIRI units are supplied in standard height (179mm≅7in.) cases, complying with IEC 297 size 4U.

The rigid case wall is manufactured from a single sheet of hot dipped galvanised steel coatedexternally with Plastisol PVC and internally with a low gloss alkyd paint finish. This constructiontechnique provides improved thermal transfer characteristics over plastic walled cases and combinesexceptional corrosion and flame resilience with good electromagnetic and electrostatic screeningproperties allowing many relays to be freely situated in close proximity and hazardous environments.When the relay is inserted a leaf spring along the top edge of the module makes contact with asolidly bonded nickel plated steel strip on the interior of the case, providing excellent earthcontinuity. This strip is brought out at the rear of the case, above the terminal block, where it forms aseparate earthing terminal. A rigid front mounting flange is provided allowing the entire range ofstandard cases to be flush mounted without alteration. These flanges are also used to mount the relayinspection cover which is secured by thumbscrews. Securely bonded channels can be provided on thetop and bottom surfaces toward the rear of the case allowing large rigid assemblies to be created bythe use of joining strips located in these channels.

This uniform but highly flexible housing system integrates excellent mechanical strength with goodelectrical practice in industry standard sizes.

PANEL CUT OUT FLUSH

MOUNTING FIXING DETAILS

4 HOLES 4.4mm DIAMETER

99

168 159

52 23.5

10

97

45

PUSH BUTTON

PROJECTION 10mm

NOT SHOWN TO SCALE

103

177

212

Clearance

25 min

157

32

OPTIONAL

OPTIONAL

OPTIONAL

Min28

NOTE Minimum gap between vertical

spacing is required in order to

withdraw relay from the case above.

178

Required to open case SIZE 100 CASE

02/05/96 MIRI 01/96I20

9.9 Terminal Connection Details

The rear terminal block accepts both pre-insulated screw and push-on blade type connectors whichmay be used singly or in combination. Each terminal has 1 screw type and 2 blade type connectors.

Screw: Each connection uses a 4mm (M4) screw outlet and accepts standardL-shaped ring type connectors designed for 4mm screws.

Blade: Each connection facilitates 2 pre-insulated push-on blades 4.8mm wide0.8mm thick complying with BS5057.

Combinations: Each terminal will accept either;2 ring type connectors

or 2 push-on blade type connectorsor 1 ring type connector & 1 push-on blade type connector

1

3

5

7

9

11

13

15

17

19

21

23

25

27

2

4

6

8

10

12

14

16

18

20

22

24

26

28

Earth

Rear terminal block connections.

Each terminal

1 screw &2 spade

MIRI

All information subject to change without noticePublication number MIRI 01/96I

02/05/96 MIRI 01/96I21

10. Order Form

Digital Overcurrent and Earth Fault Protection Relay MIRI

MIRI

Overcurrent with Earth Fault IEOvercurrent Only IEarth Fault Only ESensitive E/F ES

Rated Current 1A 15A 5

Power Supply, 24V (16-60Vac, 16-80Vdc) L 110V (50-270Vac, 70-360Vdc) H

Housing 19" Rack APanel Mounting D

PBSI Ltd Trading as

P&B ENGINEERINGBelle Vue Works,Boundary Street,Manchester.M12 5NG.

Tel: 0161- 230-6363Fax: 0161-230-6464