Siemens 7 SK 88 A Series User manual

SIEMEt~S
7 SK 88 .. - .. A
IDMTL OVERCURRENT RELAY
Installation and maintenance instructions
." .
.:
:.:
.:
:.:~: :.:
:.: :.:
.........
:.:.:.: :.:.:
:.: :.
.. "
•. w.
:.: :.:
:.: ;.;
•• ' ·w· .. "

,
I•
I
•
T
I
t
-<
t
•
: I'
" •
Protective relays
Static
single
ph as e ,
10M TL
overcurrent
rei a y
7 SK 88.
• •
.A
Installation and maintenance instructions
...
"'!f~~.
Contents
Survey of types
Description
Acceptance check
Installation
Setting the relay
Auxi I iary su pply
Commissioning
Maintenance
Technical data
Plug setting link
Page
2
3
3
3
7
10
13
15
17
Test sockets
Contact pin
Time multiplier I >
Target indicator I >
High set I»
Target indicator I»
Reset
(4) E14041-F7230-U211-Al-7600

i
I
i
:/
:\
,\
I
,
I
'f
'I
J
- 2 -
1. Survey of Types (ordering codes)
Inverse-time overcurrent relay system 7SK88 In a compact case
"
For Currel'll
Ir anslor mer
rated Curre
Setting range
of 751<88
Supply voltage UV
60 V d,c. \',0 V d.c.
Supply from
Weigl'll.
1125 V d.c
1220 V d.&:.
current
I'll
transformer
approx
Order No. Order No.
Order No_
Order No.
A A
(for the Order No, suffix see below)
kg
--
01 to 0.4 75K8.12- ••
75K"1~ .•
75K •• 14- .•
75K8.15- .•
75KII 11- ..
02 to
0_8
22- •• 2~ .•
24- .•
25- ••
21- ..
1,5
lor 5 *
lor 5 * 0,5
to
2
32- •• 3~ ••
34- .•
35- ••
31- ..
I CT. powerd
5
5
1 to 4
2_5 to 10
4 to 18
42- .. 4~ .•
52- .•
5~ ..
12- .• Uo-
••
44- ••
45- .•
41- ..
version 1,8)
54- .•
55- ••
51- ..
64- .•
a5- .•
61- ..
• In this case, the 5 A c.t. shall be in the earth fault circuit.
Thus a higher sensitivity is achieved.
Order No. suffix for7SK88
Characteristic and optional element I~
--------------------.-- --------~----
Characteristic
Short-circuit instantaneous trip I~
not fitted fitted
Order No. suffix 7SK88 •• -
-------------------------
Inverse
1DA 1EA
Very inverse
3DA 3EA
~E~x~t~r~e~m~e~1~y~~i~n~v_e_r_s_e ____ 4_D_A ______________________ 4EA
Continuous technological progress and modernisation of components
may necessitate production modifications. These modifications
do not affect relay performance and are recorded, for internal
purposes only, by two letters after the code (MLFB) number (e.g.
7SK8818-1DA/DD).
Test adapteJ for 7SK88
7XV8110
1XV8120
Test adapter cable with banana plugs
Test adapter cable with Harting plug
for testing with 7VP461
(

• - 3 -
2• Description
Relay 75K88 i~ a self contained, single phase overcurrent protec-
tion device with inverse definite minimum time characteristics.
Its applications include primary protection of radial networks
in distribution and industrial installations and back-up protec-
tion for distance relays and similar schemes.
The 7SK88 can be supplemented by the directional relay 7SP88.
This combination provides a directional inverse time protection
system for the protection of ring mains and parallel lines or
transformers.
~ It can be equipped with a high set instantaneous element. Al-
though designed principally for operation from an auxiliary d.c.
power source, a version is available for current transformer de-
rived auxiliary power, allowing use in installations where sepa-
rate d.c. power is not provided.
•
•
3.. Acceptance Check
On unpacking the relay, check the nameplate to ensure that the
model number and rating agree with the requirements. Check that
there are no signs of physical damage. The relay has been tho-
roughly works-tested and calibrated. It contains no moving parts
and is therefore ready for installation without adjustment. If
the target indicator shows "tripped" (red) when delivered, this
is unimportant since it can be reset as soon as the auxiliary
supply voltage is connected or, with the C.T. powered version,
when at least 20 J load current flows in the primary circuit.
4. Installation
The case is designed for flush mounting in a panel or support
plate of any convenient thickness (fig. 1) and at any convenient
angle in a location reasonable free from excessive heat, dust
and moisture. It can be secured by two machine screws (H6), with
nuts, top and bottom of the front bezel •

- 4 -
External connections are at the rear. These are post type ter-
minals fitted with slotted head screws and clamps. Flexible or
stranded conductors must be fitted with crimped ferrules. All
terminals are permanently numbered. For front-access-only cabi-
nets, the relays can be mounted on hinged plates or frames for
access to the terminals. The units are not sensitive to shock.
(Tested to withstand 2 G). The internal carrier is secured by
screws from the back and supports the plug-in printed circuit
board on the right hand side which carries the static component
circuitry.
CD fixing screws for internai carrier
Fig. 1:
Inverse-time overcurrent relay 7SK88; compact case
for switchboard panel flush mounting
With the current transformer short-circuited and the auxiliary
supply de-energised, connect the C.T. leads to terminals 3 and
4 and
the auxiliary supply to terminal 9 (+ ve) or terminal 7
(if 220 V model is used) and terminal 8 and 12 (- ve). The 220 V
model is fitted with a dropper resistance which is located at
the main terminals for good heat dissipation. This resistance
can attain a surface over-temperature of 200 °c - it must be
ensured that the resultant heat can properly dissipate and is
not obstructed by adjacent wiring or other restrictions.

I ~
•
•
•
, .
L+
Test cUrTent injection
T Reset
L+ lS
M
L- 1S
§
- 5 -
I = TM =0,05-0,5 Bushes on Frontplate for
II ~ TM : 0, SS -1 response time measurement
I>
Q
Br.1
Rel.A
I»
¢
ReLB
~-~ ---5chauzeichen 1:
Targetindicator -c:J- § ~ t-....:==:J J
L ___ . __ . ____ ' __ 0 p./JPo __ Br~~_. __ ._J_::'_. __ ~ __ .
4/2216
• "dropper" resistance. 220 V model only •
Fig. 2: Internal Schematic 1SK88xx-xxA
If the target indicator shows "tripped", it can now be reset on
application of the auxiliary supply or, with the C.T. powered
version, when at least 20 ~ load current flows in the primary
circuit.
With the C.T. powered version terminals 8 and 9 remain free.
In planning the tripping circuits, ensure that the rating of the
output relay contacts are not exceeded.

L1 L2 L3
J
~
II
II
I
I
r- ~
52
1\
L....
I-
DC Trip
+----4 .......-
50/51-1
52
Fig. 3:
Fig. 30
current connections
3 51-'
50-;:4
I
__ J
3
51-2
sO-2l4 3
51-4
50--4;4
_J
.
__ J
3
51-3
50-314
J
4/2214
Fig.3c
output contact connections
5 555
Alarm
4/2214
- 6 -
Fig.3b
auxiliary supply connections
(nat applicable
to C.T. powered version)
DC aux. bus
+--~----~----~------
9_
SO/51
-1
8
9*
50151
-3
8
fr terminal 7 for 220V mo del
Legend:
51 -1 o/e- relay 75K 88
51-2 ole-relay 75K 88 optional
51- 3 ole-relay 7 5K 88
51- 4 01 c-relay 7 SK 88 optional
52 Circuit breaker
50 -1 high set element, optional
SO - 2 high set element. optional
50 - 3 high set element, optional
50- 4 high set element,opti~nal
5 5 5
Auto- rec(ose
relay or
similar
or alarm
External Schematic -7SK88 Relay
d.c. powered or C.T. powered version
(
(
(

•
•
•
•
- 7 -
5. Setting the Relal
5.1 OvercurrentElement
Remove front cover by releasing captive screws top and buttom.
Removal of the cover automatically short circuits the input from
the associated current transformer and disconnects it from the
internal circuits. Thus the accessible components on the relay
front are entirely volt-free. When used for phase overcurrent
protection, one or two further 7SK88 relays are installed in the
remaining phases. These remain operative.
The overcurrent element (I ) has two settings:
Current setting (Ip) (Plug setting)
10 - 40 ~, 20 - 80 ~, 50 - 200 ~ or 100 - 400 ~ in 7 equal steps
selected by rotary link on the front plate. This setting values
on the front plate are given in amps secondary. The two screws
must be re-tightened carefully. The link must not be left in an
open position. This setting allows the overcurrent pick-up v~lue
to be selected with respect to circuit rated load and current
transformer ratio
e.g. C.T. ratio
circuit full load current
required pick-up value
(for example)
relay range
120
Ip = 200 x 5 x 1.25 = 3.75 A.
Nearest setting = 3.75 A (75 ~) •
200/5 A
120 A
1.25 x full load current
50 -200 J
(i.e. 2.5 to 10 A)

- 8 -
5.2 Time Multiplier (TM)
Set by slotted rotary dial on the front plate; two ranges are
available: 0.05 to 0.5 in steps of 0.95 (with selector plug on
PCB in position I - as set in the factory), alt. 0.55 to 1 in
steps of 0.05 (with selector plug on PCB in position II). The
adhesive strip for the T.M. scale situated on the rear of the
front plate must also be removed and fixed on the front to cover
the printed letters TM (see fig. 6). Thus the alteration of the
TM-setting range is made visible.
The TM-setting allows selection of the time scale against which
the inverse characteristic is set (see fig. 4). The intermediate
. curves given by the 0.05 steps lie between the curves shown.
The recommended
grading time between successive relays is 0.3
to 0.4 sees.
60
1
~o
30
I 20
I
!sI
10
8
6
4
3
2
1
08
0.6
0.4
0.3
0.2
0.1
0.08
0.06
0.04
0.03
0.02
00
,
r-
l-
l-
0.5
.,,"
r--- 1
-I Ij~--
. .- I -
..
I-'
- --
---
. --
I- b=
I ~
" ' =:=
. ~~
'~I.."-" ==
",~y 1-'- r-==
.~-
,. '. ::-..~ I-r-
I '
~~ .... ~-r-
TM
\.1 . ~~ I~~~R.:~
~
NI': r-.I~'
0.8
" I~ k.~~
0.6
0.5
0.9
0.7
0.4
"'
.......
~
I
..... 0.3
" I I
f"""oo.,.\
~
I No- I I ,
.........
0.2
,
~
-
...........
0.1
..........
II
...............
..........
0.0 5
, . I
I
\
I
2 3~S 10 20
lllp-
inverse (to B.S. 142)
1: Current in A
60
r
30
20
t
Is)
10
8
6
4
3
2
1
0.8
0.6
0.4
0.3
0.2
0.1
0.08
0.06
0.04
0.03
0.02
0.01
0.5
I
I
.'tt'
!J,: Pick-up setting in A
TM: Time multiplier adjustable on front panel. to B.S. 142
,
I
:Ir.'~r-
I 'Lj-o- r --f-- -
! ~ It f--r- §
I " t t-r-
I. - =~
i 1-f--
i-e-
~
~
- - '-r-
-+-==~
\\
- r-
I \'\" I --
\\'~~t
~.
--
\. ,\~
.--
-
~
,-
-
\:\\'\.
\!..
.-
-
1\ 1\ \ \\~~"\..
\ \i\\.~.~
~
~~-
\\ ~\i\'~
\
I\\K~
, .
d,
'\
\.
\
'\I
"-
N ,
,
I
~
N
t~
1\
I
INJ
, , H
I I
I
~~
~.~
'"""'-
~
~
~
..........
'-
r-
"'"
-"""t--
:1-
-
.......
,
........
.-
r-
1M
1.0
0.9
0.7
..M..
0.6
0.5
0.4
0.3
0.2
0.1
o. 05
2 .3 .. 5 10 20
lIJp -
very inverse
Fig. 4:
Overcurrent time characteristics:
t = f II/Ip) for the inverse-time
overcurrent relay 7SK88
3 'I
1\ 1\ \.\~
elllremely Inverse
()
o
o
o

•
•
•
..
•
i
•
•
I 0·05 - O· 5
II O· 55- 1· 0
TM
-:0:·
0,05 0,5
0.05 to 0.5
(as delivered)
- 9 -
TM + 0,5 adhesive strip
"·0:'
0,05 0,5
0.5 to 1
(altered)
Fig. 5: TM range
selector
plug
Fig. 6:
TM setting range
5.3 Instantaneous Element (I»)
When fitted, is set by slotted rotary dial on the front plate:
Range: 4 to 20 times 1p. The setting is continuous
i.e. if 1p set at 3.75 A = 125 % circuit r.1.c. (as in current
setting example) and I» set on 10, then instantaneous
element operates at 37.5 A (12.5 x f.l.c.) within approx.
15 ms.
If the operating time proves to be too short, it can be extended
by inserting a capacitor, on the solder tags marked C12 on the
printed circuit board. A dry type tantalum capacitance is recom-
mended (e.g. Siemens UBB-B45178). The required capacitance for
a particular time delay is given in fig. 7; a 30 V device is
adequate •
If the solder bridge 2 is inserted on the p.c.b. then the trip
from the high set element I is blocked (as delivered the bridge 2
is not inserted) •