Midos
Type MCVG 61 Voltage Dependent Overcurrent Relay
Features
Site selection of characteristics for voltage restrained or voltage controlled overcurrent
Wide setting range
Green led start indicators to facilitate testing
Low ac burden
DC power supply operates over a wide input range
Separate test mode with trip test feature
Non volatile memory for led trip indication
Figure 1: Type MCVG 61 relay relay withdrawn from case.
Models available MCVG 61 versions are available for phase-neutral and phase-phase connection.
Application For backup overcurrent protection of generators, ordinary overcurrent relays are sometimes difficult to apply, due to the decaying characteristic of the fault current. The value of the fault current will be progressively reduced due to armature reaction, to a value less than full load current. Therefore, normal overcurrent relays, set above the load current or maximum permissible overload, cannot be applied to provide time delayed backup protection as they will not operate for these fault conditions. For successful application of generator backup protection, the operating characteristics of the relay
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are required to be a function of voltage and current. There are two types of relay that are customarily used for these applications, namely voltage restrained and voltage controlled overcurrent relays. With voltage restrained overcurrent relays, when the voltage falls below a set value, the operating time of the overcurrent characteristic is continuously reduced with declining voltage. In voltage controlled overcurrent relays, the operating time characteristic is changed from the load characteristic to the fault characteristic when the voltage falls below a set level. The MCVG 61 is a three phase voltage dependent overcurrent relay with both voltage restrained and voltage controlled characteristic available from the same relay. The desired mode is selected by a switch on the front of the relay.
Description Type MCVG 61 relays consist of a microcontroller microcontroll er based overcurrent element (identical to MCGG relays, see R6054) with one element available for each phase. The current measurement is performed by an analogue to digital converter (ADC) which forms an integral part of the microcontroller, microcontroll er, the program in the microcontroller microcontroll er constantly samples the output of the ADC and compares the value with a predetermined reference. If the output of the ADC remains above the reference value, then the microcontroller microcontroll er will give a trip signal after a time delay, which is determined by the algorithm for the selected time delay characteristic. When a trip signal is given, the trip led is set to ‘on’ and the state remembered in the non volatile EEPROM. This ensures that, if the power to the relay is lost, the trip
indication will revert to the last state on re-applying the auxiliary power. Voltage controlled and voltage restrained overcurrent is achieved by controlling the amount of current seen by the overcurrent detectors.
Voltage Controlled Overcurrent Mode In this mode the MCVG 61 operates with the load characteristic above a set voltage level. Below this voltage the relay operates with the fault characteristic. Voltage controlled overcurrent is achieved by the use of voltage level detectors. The principle of operation is that, if the instantaneous amplitude of the input voltage exceeds a preset threshold setting during any half cycle, a timer t1 is started. If t1 times out before the signal has fallen below the reference voltage, the output of the latch is set high. This latch turns the analogue switch on, which diverts current from the overcurrent measuring circuit to give the overload characteristic. When the input voltage falls below the preset threshold setting during any half cycle, a timer t2 is started. If t2 times out before the signal has exceeded the preset reference voltage, the output of the latch is set low. Resetting the latch causes the analogue switch to turn off resulting in the measuring circuit giving the fault characteristics. Voltage Restrained Overcurrent Mode In the voltage restrained mode the MCVG 61 operates on the load characteristic above 90%Vn. Below that voltage the relay pick up is reduced, depending on the magnitude of the reduction in the relay voltage. Thus the relay has a load characteristic during healthy conditions and a family of characteristics during fault conditions, when the voltage is less than 90%Vn. Voltage restrained overcurrent is achieved by taking the TRMS value of the input voltage. If this voltage is between the limits of 0.9Vn>V>0.55Vn, a voltage proportional to the input voltage is applied to the analogue switch. This diverts a proportion of the input current from the measuring circuit resulting in a gradual transition from fault characteristic to overload characteristic with increasing voltage.
Power for the relay is supplied by a dc to dc converter which is designed to work over a large voltage range. This allows one relay to cover several battery voltages. The dc to dc converter gives totally isolated outputs giving a high degree of noise immunity to the relay.
Relay Settings Separate setting switches are provided for each phase on the relay front plate. These are used to select the required time/current characteristic, voltage restrained or voltage controlled operation, overload and fault setting current, voltage controlled voltage setting and time multiplier settings.
Selection of time characteristics The time/current characteristic selection is carried out by means of three switches identified by the ( ) symbol on the nameplate. Table 1 gives the basic operating characteristics and the settings of these switches. The time given by each of the operating time characteristics must be multiplied by the time multiplier to give the actual operating time of the relay. This control is marked xt = ∑ where ∑ is the sum of all the switch positions. The range of multiplication is 0.05 to 1.0 in steps of 0.025. This acts as a convenient time multiplier on the current dependent characteristics and gives the following ranges for the definite time characteristics:
Operating characteristics (seconds)
Time range (seconds)
2 4 8
0.1 to 2.0 in 0.05 second steps 0.2 to 4.0 in 0.1 second steps 0.4 to 8.0 in 0.2 second steps
Switch position (0) (1)
Operating characteristic
Trip test
Standard inverse
sec SI
Very inverse
sec VI
Extremely inverse
sec EI
Long time earth fault
sec LT
Definite time 2 seconds
D2
Definite time 4 seconds
D4
Definite time 8 seconds
D8
Table 1: Operating time characteristics with corresponding switch positions, where I is the current applied to the relay.
3
100
10 Definite 8 seconds
) s d n o c e s ( t e m i t g n i t a r e p O
Definite 4 seconds Longtime standby earth fault t= 120 I
– K ∆I s I
Definite 2 seconds
s
–1
Standard inverse 0.14 t= I – K ∆I s 0.02 –1 Is 1.0
Very inverse t=
13.5 I – K ∆I s I
s
Extremely inverse 80 t= I – K ∆I s 2 I
s
–1
–1
0.1 1.0
10
100 I
– K ∆I s I
Figure 2: Time delayed overcurrent, operation time characteristic.
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s
s t t c u t a p n p t i r u o T o c
5 3 4 3 3 3
9 2
0 3
1 L 2 R 1 1 L R t t s u i p u h t c u i r P O c
s > I I
s >
s >
I
I
I
p i r T
p i r T
I
p i r T
n e i o v r t c u l e C e s
n e i o v r t c u l e C e s
C µ
s
∆
µ
s
s
µ
s
V
t
I
∆
n o e i d t o c e l M e s
s
V
s
n o e i d t o c e l M e s
s
I
V
V
s
I
V
>
>
A h P
C
t
∆
I
A h P
C I
n o e i d t o c e l M e s
s
V
n e i o v r t c u l e C e s
A h P
t
I
t e s e R
2 1 L R
> n o i t c e n n o c h t r a e e s a C
s r l y i e p t w p u c r o u i P s c
7 3
8 1 3 2
2 2
1 4
2 3 4 2
4 2
5 4
6 5 4 2
B
A
E E V V + –
C
I
I
6 3 4 2 1 1 1 I
x
V
1 S
1 P
2 P
2 S C
c
B
b
A
A
N n
1 e t o N e e S
a
B C
0 3
4 6 8 3 3 3
2 4
6 8 0 4 4 5
9 2
3 5 7 3 3 3
1 4
5 7 9 4 4 4
B
A
C
h t r a e e s a C
1
4 1
2 2
4 2
6 2
8 2
3 1
1 2
3 2
5 2
7 2
) p a r t k s c r h o l a t b e r l r a e a n m e i s o r a m f r c e d l t a e e r l u w e g e d i t v n o i M h t i w (
. ) c . ( t c e e r o n f n e b e o c k i s k a d a m ) e r s c b k ( s . s n d l l i l n a a n n a i g ) i n m m i t ( r r b e r e o e t t r t h s f g o r o T e h n o C b S L
. y l n o l a c i p y t e r a s n o i t c e n n o c g n i h t r : s a ) a e E ( t o N 1
) ) c b ( (
. y l n o l a c i p y t e r a s n o i t c e n n o c T C 2
. ) s n o i t a i r a v w o h s 3 d n a 2 s t e e h s 2 0 1 6 G V C M 0 1 s m a r g a i D ( . D e u s s i 1 t e e h s 2 0 1 6 G V C M 0 1 m a r g a i d n o i t a c i l p p A : 3 e r u g i F
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Technical Data Ratings AC current (I n)
1A or 5A
AC voltage (Vn)
110V or 63.5V
Rated frequency
50Hz or 60Hz
DC Auxiliary voltage (Vx)
24/54V or 110/250V
Burdens AC current
Less than 0.25V for 1A relays and less than 0.5VA for 5A relays at unity power factor and at rated current on any setting. The impedance of the relays over the whole of the setting range is less than 0.25Ω for 1A relays and less than 0.2Ω for 5A relays and is independent of current.
AC voltage
Less than 0.1VA at rated voltage
DC voltage
Relay rating
Burden
24/54V 110/250V
8.5W 11.5W
The figures above are maxima under quiescent conditions. With output element operated they are increased by up to a maximum of 3W.
Setting ranges Voltage setting
55% to 90% Vn in steps of 5% Vn
Voltage control mode Current pick up level
I
I
s
∆I s
s + K∆I s
K = 0 when VVs
5% to 240% I n
in steps of 5% I n
50% to 200% I n
in steps of 10% I n
Where V is the applied ac voltage Drop off to pick up ratio of under voltage detector
>107%
Voltage Restrain mode Current pick up level
I
s + K∆I s
K=1
when V>90% Vn
(V/Vn – 0.55) ( 0.35 ) when 55% Vn
I
s
∆I s
K=0
when V<55% Vn
5% to 240% I n
in steps of 5% I n
50% to 200% I n
in steps of 10% I n
Where V is the applied ac voltage
Operating time Time delayed element
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See Figure 2
Operating characteristics IDMT Characteristics
Standard inverse Very inverse Extremely inverse Long time earth fault
Definite time delays
2, 4, 8 seconds
Time multiplier
0.05 to 1.0 in 0.025 steps (applicable to all characteristics)
Operation indicators
Each phase is provided with a red led indicator. The trip indication is non volatile. If the auxiliary power supply is lost the trip indicator will be in the last state when the power supply is reinstated. The green indicator illuminates when the input current for the appropriate phase exceeds the current pick-up level of I s + K∆I s, and resets when the phase current falls below the resetting current.
Accuracy
Input current
Reference conditions:
Reference range:
Current setting (I s) ∆I s setting Vs setting K value Ratio of ∆I s: I s
0.05 I n to 2.4 I n 0.5 I n to 2.0 I n 0.55 Vn to 0.9 Vn 0 to 1 for voltage restrain mode 0 or 1 for voltage control mode less than 5 : 1
Time characteristic:
Reference range:
Standard inverse Very inverse Long time inverse
K∆I s + (2 x I s to 31 x I s)
Extremely inverse
K∆I s + (2 x I s to 20 x I s)
Definite time
K∆I s + (1.3 x I s to 31 x I s)
Ambient temperature
20°C
Frequency
50Hz or 60Hz
Time multiplier setting 1x DC auxiliary voltage
Reference range: 24V to 54V 110V to 250V
Accuracy – influencing quantities Time multiplier
On settings 0.05 to 1.0: 5% or 50ms whichever is the greater
Ambient temperature
Operative range: –25°C to +55°C Variations over this range: I
s setting: ± 5%
∆I s setting: ± 5%
K value: ± 0.05 (in voltage restrain mode only) Vs setting: ± 1%
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Time characteristic
Time variation
Standard inverse Very inverse Long time inverse
± 5%
Extremely inverse
± 7.5%
Definite time
Frequency
± 5%
I s setting: ± 1% over the range 47Hz to 52Hz or 57Hz to 62Hz
∆I s setting: ± 1% over the range 47Hz
to 52Hz or 57Hz to 62Hz K value ± 0.05 over the range 47Hz to 52Hz or 57Hz to 62Hz (in voltage restrain mode only) Vs setting: ± 7.5% over the range 47Hz to 52Hz or 57Hz to 62Hz Operating time: ± 7% or 50ms whichever is the greater over the range 47Hz to 52Hz or 57Hz to 62Hz DC auxiliary voltage
Vx (V)
Operative range (V)
24/54 110/250
19 to 65 87.5 to 300
Variations over these ranges: I
s setting: ± 5%
∆Is setting: ± 5%
K value: ± 0.05 (in voltage restrain mode only) Vs setting: ± 1% Operating time: ± 7.5% or 50ms whichever is the greater
Accuracy – general I
s setting: 1.0 x I s to 1.1 x I s
∆I s setting: ± 5% for ∆I s:I s<2:1 ∆I s setting: ± 10% for 2:1<∆I s:I s<3:1 ∆I s setting: –10% +20% for 3:1<∆I s:I s<5:1
K value: ± 0.05 (in voltage restrain mode only) Vs setting: ± 5% Operating time
Time characteristic
Accuracy
Standard inverse Very inverse Long time inverse
± 5%
Extremely inverse
± 7.5%
Definite time Repeatability (within basic accuracy claim)
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Pick up current I s + K∆I s
better than 2%
Operating time
better than 3% or 30ms whichever is greater
± 5%
Overshoot time
less than 50ms (When the input current is reduced from any value within the operative range to zero)
Resetting current
Not less than 95% of time delayed current setting
Resetting and disengaging
Less than 70ms (when the input time current is reduced from any value within the operative range to zero)
Transient overreach
System time constant up to 30ms: 5%
Contacts
1 changeover self reset 1 normally open self-reset
Contact ratings Make and carry continuously
ac 1250VA with maxima of 5A and 660V dc 1250W with maxima of 5A and 300V
Make and carry for 0.2s
ac 7500VA with maxima of 30A and 300V dc 7500W with maxima of 30A and 300V
Break
ac 1250VA with maxima of 5A and 300V dc 50W resistive 25W inductive with L/R = 40ms subject to maxima of 5A and 300V
Durability Loaded contact
10,000 operations minimum
Unloaded contact
100,000 operations minimum
Current transformer requirements Relay and CT secondary rating
1A
5A
Nominal output
2.5VA
7.5VA
Accuracy class
10P
10P
Accuracy limit (x rated current)
20
20
Limiting lead resistance – one way
1Ω
0.15Ω
Thermal withstand Continuous withstand
2 x I s or 2.6 x I n whichever is lower, with a minimum of 1 x I n
Voltage
1.2 x Vn
Short time withstand Current
For 1 second: 100 x I n with 400A maximum. For 3 seconds: 57 x I n with 230A maximum.
Voltage
2 x Vn for 30 seconds
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High voltage withstand Dielectric withstand IEC 255-5: 1977
2kV rms for 1 minute between all terminals and case earth. 2kV rms for 1 minute between terminals of independent circuits including contact circuits, with terminals on each independent circuit connected together. 1kV rms for 1 minute across open contacts of output relays.
High voltage impulse IEC 255-5: 1977
Three positive and three negative impulses of 5kV peak, 1.2/50µs, 0.5J between all terminals and case earth
Electrical environment DC supply interruption IEC 255-11: 1979
AC ripple on dc supply IEC255-11: 1979 High frequency disturbance IEC 255-22-1: 1988 Class III
Electrostatic discharge IEC255-22-2: 1989 Class II IEC801-2: 1991 Level 2 Fast transient disturbance IEC255-22-4: 1992 Class III IEC801-4: 1988 Level 3 EMC compliance 89/336/EEC EN50081-2: 1994 EN50082-2: 1995
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The unit will withstand a 10ms interruption in the auxiliary supply, under normal operating conditions, without de-energising. The unit will withstand 12% ac ripple on the dc supply. 2.5kV peak between independent circuits and case. 1.0kV peak across terminals of the same circuit. 4.0kV discharge in air with cover in place. 4.0kV point contact discharge with cover removed. 2.5kV, 5kHz applied directly to auxiliary supply. 2.5kV, 5kHz applied directly to all inputs.
Compliance with the European Community Directive on EMC is claimed via the Technical Construction File route. Generic standards were used to establish conformity.
Atmospheric environment Temperature IEC255-6: 1988 IEC68-2-1: 1990 IEC68-2-2: 1974
Storage and transit –25°C to +70°C Operating –25°C to +55°C Cold Dry heat
Humidity IEC68-2-3: 1969
56 days at 93% RH and 40°C
Enclosure protection IEC529: 1989
IP50 (dust protected)
IEC1010-1: 1990/A2: 1995 Polution degree 2
Equipment designed for environments where only non-conducting pollution occurs. Occasionally light condensation may be expected.
EN 61010-1: 1993/A2: 1995 Pollution degree 2
Mechanical environment Vibration IEC255-21-1: 1988
Response Class 1 Endurance Class 1
Case information Type MCVG 61 relays are housed in size 8 cases. See Figure 4 for dimensions.
200
155.4
4 holes Ø 4.4
24
Information required with order
159
168
Relay type Rated current Rated voltage Frequency Rated auxiliary voltage
Push button projection 10 max.
203 Panel cut-out: Flush mounting fixing details.
32
25 min.
157 max.
177
206
212
Reset Flush mounting.
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All dimensions in mm. Figure 4: Case outline size 8.
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