ABB SPAM 150 C - Example 3. Protecting a Direct Started Motor with a Low Safe Stall Time

11
L1
L2 L3
Uaux
Internal Relay Fault
+
-
Motor Restart Enable
Startup Information from Motor
Thermal Prior Alarm
Signal for Tripped Motor
Trip Output Relay
63
6261
1 A
5 A
1 A
5 A
1 A
5 A
252627
123456789
1 A
5 A
70 71 72
Rx Tx
65
66
IRF
68 6977 7874 75
80 81
10
11
1 1
SGB/1
SGB/2
SGB/7 SGB/8
SGB/3
TRIP
R
SEAL-IN
Σ >
ts
1
+
B
+
C
+
F
+
E
+
D
+
A
3
SGB/4
STALL
I/O
I»
Io>
I<
START
∆I
I t
2
RESTART INHIBIT
RESTART INHIBIT
SGB/5
RELAY RESET
θ>θ
i
θ>θ
a
θ>θ
t
SGB/6
EXTERNAL TRIP
U1 SPCJ 4D34
U3 SPTK 4E3
U2 SPTU _ R2
s
s
BLOCK DIAGRAM WITH FACTORY SETTINGS OF SWITCHES SGR
SPAM 150 C
I
0
–
+
Example 3
Protecting a
direct started
motor with a low
safe stall time
In many applications, e.g. ExE-type drives, the
motor is not allowed to be in a stalled condi-
tion as long as its own start-up time. To find
out whether the motor is speeding up or not, a
speed switch on the motor shaft is used. The
switch should be open at standstill and close
when the motor speeds up.
The speed switch information is used to control
the start-up stress monitor and the setting ts is
set a little shorter than the maximum allowed
jam time t
e
. If the motor starts accelerating, the
speed switch will inhibit the start-up supervision
unit trip and leave the protection to the thermal
unit. If the motor does not speed up, tripping
will be carried out after the time t
s
= t
e
.
The speed switch should be open at standstill and close when the motor speeds up.
Fig. 7. Protection of a directly started motor. A speed switch on the motor is used to produce a
secure stall protection even though the maximum safe stall time of the motor is less than the start-
up time.
Note that because of the fact that only two phase CTs are used, the third phase is reconstructed by
summing the two monitored currents through the third winding.