The ground differential protection function (Br.: restricted earth fault protection) can be applied to transformer windings with grounded neutral point where the neutral point-to- ground connection is fitted with a current transformer.
The ground differential protection (Br: restricted earth fault protection) function is not provided by the P631. For the other P63x models, one ground differential protection function per transformer winding is available for up to three ends. The P63x display shows the winding end associated with a particular ground differential protection function. Connection for and operation of the ground differential protection function will now be presented with end 'a' as an example. Equivalent considerations apply to ends 'b' and 'c'.
Ground differential protection may be applied to transformer ends with a grounded neutral-point, but in this case the neutral-point-to-ground connection must be fitted with a CT.
Ground differential protection is based on comparing the vector sum IN of the phase currents of the relevant transformer end to the neutral-point current IY. The P63x calculates the vector sum of the phase currents. For the connection, see section 'Conditioning of the measured values'.
Disabling or enabling ground differential protection
Ground differential protection can be disabled or enabled using setting parameters.
Moreover, enabling can be carried out separately for each parameter subset.
3-93 Disabling or enabling ground differential protection
P63X/EN M/Ba4 // AFSV.12.09701 D /// P631-305-403/404-610 // P632-305-403/404-610 // P633-305-404/405/406-610 // P634-305-403/404-610 3-147 Amplitude matching
For amplitude matching, the nominal power of the transformer end should first be set as the reference power. The reference current is then calculated by the P63x on the basis of the set reference power and the set primary nominal voltage of the transformer end.
a , nom a ref
, N ef,
r V
I S
= ⋅ 3
Sref: reference power
Iref,N,a: reference current of the ground differential protection function, end a Vnom,a: nominal voltage, end a
The P63x calculates the matching factors on the basis of the reference currents and the set primary nominal currents of the system transformers.
a , N ef, r
a , nom a , N ,
am I
k = I
a N, ef, r
a , Y , nom a , Y ,
am I
k =I
with
am: amplitude-matched
Inom,a: primary nominal current of the main current transformer
Inom,Y,a: primary nominal current of current transformer in the neutral-point-to-ground connection
Reference currents and matching factors are displayed at the P63x.
The P63x checks that the reference current and matching factor are within their permissible ranges. The acceptable range for the reference current can be read out from the S&R 103 operating program. The following applies to the matching factors:
The matching factor must always be ≤ 16.
The value for the smaller matching factor (kam,min) must always be ≥ 0.5.
Should the P63x calculate a reference current or matching factors not meeting the above conditions then an alarm will be issued and the P63x will be blocked automatically.
The measured values are multiplied by the relevant matching factors and are then available for further processing. Consequently, all threshold values and measured values always refer back to the relevant reference current rather than to the transformer nominal current or the nominal current of the device.
kam,N,a > 16
kam,N,a > 16 kam,N,a =
kam,N,a =
64Z6020 A_EN REF_1: Matching fact. kam,N [ 004 160 ] REF_1: Matching fact.kam,Y [ 004 163 ] SFMON: Match.f.
kam,N REF_1 [ 091 101 ] SFMON: Match.f.
kam,Y REF_1 [ 091 102 ]
SFMON: Min.mtch.
f.inv.REF_1 [ 091 104 ] Inom,a/
Iref,N,a Inom,Y,a/
Iref,N,a
Monit. range limits Iref,N,a=Sref/
(Vnom*©3)
REF_1: Reference power Sref
[ 019 031 ] MAIN: Vnom
prim., end a [ 019 017 ]
MAIN: Inom C.T.prim.,end a [ 019 020 ] MAIN: Inom C.T.Yprim,end a [ 019 027 ]
kam,min < 0.5 kam,min
REF_1: Ref. curr.
Iref [ 019 034 ] SFMON: Inv.range Iref REF_1 [ 091 105 ]
3-94 Calculating and monitoring the matching factors
P63X/EN M/Ba4 // AFSV.12.09701 D /// P631-305-403/404-610 // P632-305-403/404-610 // P633-305-404/405/406-610 // P634-305-403/404-610 3-149 Operating modes
As of version P63x -603 a new parameter makes it possible for the user to choose among three operating modes.
Address Description Range of Values PS1 PS2 PS3 PS4
072 149 073 149 074 149 075 149 EDIF1: Operating mode PSx Low imped. / sum(IP) Low imped. / IP,max High impedance 072 169 073 169 074 169 075 169 EDIF2: Operating mode PSx Low imped. / sum(IP)
Low imped. / IP,max High impedance 072 049 073 049 074 049 075 049 EDIF3: Operating mode PSx Low imped. / sum(IP)
Low imped. / IP,max High impedance
The 'Low imped. / sum(IP)' operating mode is the same as the (low impedance) ground differential protection function previously provided by version P63x -602.
'Low imped. / sum(IP)' operating mode
From the amplitude-matched resultant currents Iam,N,a and Iam,Y,a , the differential and restraining currents are calculated as follows:
a Y, , am a N, , am a , N ,
d I I
I = +
a N, , a am N, ,
R I
I =
Again, the equation for the differential current applies under the condition of uniformly defined current arrows relative to the protected object. Both current arrows point either towards the protected object or away from it.
Figure 3-95 shows the tripping characteristic of the ground differential protection function. The characteristic equation is as follows:
a , N , ref
a N, , R a
, N , ref
a N, , diff ref
a , N , d
I . I I
I I
I = > +1005⋅
with
Idiff>,N,a: setting at R E F _ 1 : I d i f f > P S x
P63X/EN M/Ba4 // AFSV.12.09701 D /// P631-305-403/404-610 // P632-305-403/404-610 // P633-305-404/405/406-610 // P634-305-403/404-610 3-151 Fault current cha
racteristic
for transient satura tion of
the main current transformers
Id,N> / Iref = 0.2 Id,N / Iref
IR,N / Iref
12201e.DS4
m = 1.005
Tripping area
Blocking area
2.00 4.00 6.00 8.00
0.00 2.00 4.00 6.00 8.00
3-95 Tripping characteristic of ground differential protection with the 'Low imped. / sum(IP)' operating mode
'Low imped. / IP,max' operating mode
Using this operating mode differential current Id and restraining current IR are defined as follows:
{ }
{ }
( am,P A B C am,Y Y)
R
Y Y , C am B P A
, am d
I k I , I , I max k
I
I k I , I , I k
I
⋅ +
⋅
⋅
=
⋅ + Σ
⋅
= 2 1
When compared to the 'Low imped. / sum(IP)' operating mode, a double slope tripping characteristic can be used here because of the definition of the restraining current (see Figure 3-96). In particular, this tripping characteristic permits a tripping test under load current by shorting a phase current (to simulate residual current) without the need of star point current IY.
Besides the Idiff> parameter, already available to set the basic pick-up sensitivity, the following parameters are also provided with the 'Low imped. / IP,max' operating mode to set the tripping characteristic; in this case IR,m2 is equivalent to Iref.
Address Description Range of Values PS1 PS2 PS3 PS4
072 162 073 162 074 162 075 162 REF_1: m1 PSx 0.00 … 0.20 … 1.00 072 163 073 163 074 163 075 163 REF_1: m2 PSx 0.15 … 1.50 072 164 073 164 074 164 075 164 REF_1: IR,m2 PSx 0.10 … 1.00 … 1.50 072 172 073 172 074 172 075 172 REF_1: m1 PSx 0.00 … 0.20 … 1.00 072 165 073 165 074 165 075 165 REF_1: m2 PSx 0.15 … 1.50 072 166 073 166 074 166 075 166 REF_1: IR,m2 PSx 0.10 … 1.00 … 1.50 072 192 073 192 074 192 075 192 REF_1: m1 PSx 0.00 … 0.20 … 1.00 072 193 073 193 074 193 075 193 REF_1: m2 PSx 0.15 … 1.50 072 194 073 194 074 194 075 194 REF_1: IR,m2 PSx 0.10 … 1.00 … 1.50
P63X/EN M/Ba4 // AFSV.12.09701 D /// P631-305-403/404-610 // P632-305-403/404-610 // P633-305-404/405/406-610 // P634-305-403/404-610 3-153 Idiff>
Id/Iref
m 2
1 1.5 2
0.5 0.5
1 1.5
IR/Iref 2
m 1
IR,m2 Fault current characteristic for
single-end, single-phase infeed
64Z6021A_EN
3-96 Tripping characteristic of the ground differential protection with the 'Low imped. / IP,max' operating mode
'High impedance' operating mode
This operating mode is provided for application with the high impedance current measuring approach. The pick-up sensitivity is set via the Idiff> parameter which is already available.
Idiff>>> threshold
The restraining quantity is no longer taken into account when the differential current value exceeds the threshold set at R E F _ 1 : I d i f f > > > P S x . Therefore the P63x will issue a trip signal independently of the restraining quantity.
Applying Current
Transformer Supervision
When applying current transformer supervision (CTS) (as of version P63x -606), the ground differential protection function may be blocked for the relevant end where a CT fault is detected. See details given in the section describing the CTS function group.
When a C T S : A l a r m e n d y signals is issued, the associated ground differential protection function is then blocked, if if it has been set accordingly
(R E F _ n : C T S e f f e c t i v e P S x = 'Yes' by assigning REF_n to end y).
P63X/EN M/Ba4 // AFSV.12.09701 D /// P631-305-403/404-610 // P632-305-403/404-610 // P633-305-404/405/406-610 // P634-305-403/404-610 3-155
64Z6022 A_EN IN,a
REF_1: IR,m2 PSx
[ * ] REF_1: m2 PSx
[ * ] REF_1: m1 PSx[ * ] REF_1: Idiff>
PSx
[ * ]
REF_1: Idif>>>
PSx
[ * ] kam,N,a*IN,a
kam,Y,a*IN,a
Id,N,a
IR,Y,a
REF_1: Trip signal [ 041 005 ]
REF_1: IR,N,a
402 551
REF_1: Id,N,a
402 550
MAIN: Protection active
306 001
REF_1: Enabled [ 041 132 ]
IA, a IB, a IC, a IY, a
Parameter set 1 set 2 set 3 set 4
DIFF: m2 PSx 072 163 073 163 074 163 075 163 REF_1: m1
PSx 072 162 073 162 074 162 075 162 REF_1: Idiff>
PSx 072 150 073 150 074 150 075 150
REF_1: IR,m2 PSx 072 164 073 164 074 164 075 164
REF_1: Idiff>>>
PSx 072 151 073 151 074 151 075 151 CTS: Alarm end a
[ 036 205 ] 1: yes REF_1: CTS effective [ 080 003 ]
1: yes
3-97 Measuring system of the P63x
Measured operating data of ground differential protection
The differential and restraining currents are displayed as measured operating data provided that the set thresholds are exceeded.
3-98 Measured operating data of differential and restraining currents