Technical data

Siemens SIP · 2008
12 Motor Protection / 7SK80
12
12/14
Protection functions
Flexible protection functions
The 7SK80 enables the user to easily add
up to 20 additional protective functions.
Parameter definitions are used to link
standard protection logic with any chosen
characteristic quantity (measured or calcu-
lated quantity) (Fig. 12/10). The standard
logic consists of the usual protection ele
-
ments such as the pickup set point, the set
delay time, the TRIP command, a block
function, etc. The mode of operation for
current, voltage, power and power factor
quantities can be three-phase or single-
phase. Almost all quantities can be oper
-
ated with ascending or descending pickup
stages (e.g. under and over voltage). All
stages operate with protection priority.
Protection functions/stages available are
based on the available measured analog
quantities:
Function ANSI No.
I<37
I>, I
E
> 50, 50N
V<, V>, V
E
> 27, 59, 64
3I
0
>, I
1
>, I
2
>, I
2
/I
1
3V
0
>, V
1
><, V
2
><
50N, 46
59N, 47
P><, Q>< 32
cos ϕ (p.f.)>< 55
f>< 81O, 81U
df/dt>< 81R
For example, the following can be imple
-
mented:
•
Reverse power protection (ANSI 32R)
•
Rate-of-frequency-change protection
(ANSI 81R)
Trip circuit supervision (ANSI 74TC)
One or two binary inputs can be used for
monitoring the circuit-breaker trip coil
including its incoming cables. An alarm
signal occurs whenever the circuit is gener-
ated. The circuit breaker trip coil is moni-
tored in the open and closed position.
Interlocking features can be implemented
to ensure that the beaker can only be closed
if the trip coil is functional.
Lockout (ANSI 86)
All binary output statuses can be memo-
rized. The LED reset key is used to reset
the lockout state. The lockout state is also
stored in the event of supply voltage fail
-
ure. Reclo- sure can only occur after the
lockout state is reset.
Thermal overload protection (ANSI 49)
To protect cables and transformers, an
overload protection function with an
integrated warning/alarm element for
temperature and current can be used.
The temperature is calculated using a
thermal homogeneous body model
(per IEC 60255-8), it considers the energy
entering the equipment and the energy
losses. The calculated temperature is con
-
stantly adjusted according to the calculated
losses. The function considers loading his
-
tory and fluctuations in load.
Protection of motors require an additional
time constant. This is used to accurately
determine the thermal heating of the stator
during the running and motor stopped con
-
ditions. The ambient temperature or the
temperature of the coolant can be detected
either through internal RTD inputs or via
an external RTD-box. The thermal replica
of the overload function is automatically
adapted to the ambient conditions. If nei-
ther internal RTD inputs nor an external
RTD-box exist, it is assumed that the ambi-
ent temperatures are constant.
Settable dropout delay times
If the relays are used in conjunction with
electromechanical relays, in networks with
intermittent faults, the long dropout times
of the electromechanical relay (several
hundred milliseconds) can lead to prob
-
lems in terms of time coordination/grad
-
ing. Proper time coordination/grading is
only possible if the dropout or reset time is
approximately the same. This is why the
parameter for dropout or reset times can
be defined for certain functions such as
time-overcurrent protection, ground
short-circuit and phase-balance current
protection.
Fig. 12/10 Flexible protection functions