Allen-Bradley LSIG-MM User Manual

(21) DIR 1000587R0002 (Version 02)
3.6. Protection functions
LSIG-MM handle numerous independent protection functions.
The current and internal temperature signals are processed by the trip unit which, depending on the protection parameter settings,
indicates alarms, performs delay processes and sends commands.
The various types of adjustable protections are managed by the trip unit in different ways:
- The current protections are processed according to the true root mean square value of the current values read by the current
sensors.
- The temperature protection is monitored by means of the internal sensor of the trip unit.
The Iinst fi xed protection is also available and can neither be disabled nor adjusted.
The Protections menu also allows the operator to view and edit all the available parameters.
Protections Options available
Trip unit
LSIG-MM
Protection L Threshold, Time, Curve, Thermal memory S
Protection S Enabling, Threshold, Time, Curve, Thermal Memory, Startup S
Protection I Enabling, Threshold, Startup S
Protection G Enabling, Threshold, Time, Curve, Trip enabling, Startup S
Protection U Enabling, Threshold, Time, Curve, Trip enabling S
Protection T Enabling S
Load protection Enabling and threshold (1), Enabling and threshold (2), Enabling and threshold (Iw) S
Neutral Protection Enabling, Threshold S
(1)
Protection MM Enabling, Threshold S
Key:
S : standard protection
O : optional function
Notes:
1. : function available with four-pole CB, or three-pole CB in the 3P+N confi guration
NOTE: 3.6.2 through 3.6.11 explains each of the protection functions independently. Actual behavior of a circuit breaker depends
on combination of settings for each protection function and is summarized in 3.6.12.
3.6.1. Notes about Protection Operation
LSIG-MM is equipped with “backup-protection”. If the fi rst command to the trip coil fails to open the circuit-breaker immediately
(TC locked), further trip commands are transmitted until the circuit-breaker opens.
The declared tolerance values of the measurements and protections of the trip unit could change if the electrical characteristics
of the current signals fail to comply with the limits specifi ed in chapter 3.3.8.
3.6.2. Protection L
Protection L is the only protection that cannot be disabled since it provides self-protection against circuit-breaker overloads. The
types of trip curves settable are divided into two groups according to the standard they refer to.
Standard trip curve according to IEC 60947-2
Only one type of curve is settable (t=k/I
2
) as defi ned by the IEC standard 60947-2.
The tripping time is calculated in relation to the value of If:
- For fault currents If 12ln, the tripping time of the protection is given by the expression: t(s)= . If the calculated value is
less than 1 second, the real tripping time is forced to 1 second (t(s)= 1s.).
- For fault currents If >12ln, the tripping time is always t(s)= 1s.
Standard trip curve according to IEC 60255-121
3 types of curve settings can be made and are defi ned by standard IEC60255-121 as A, B and C.
The protection trip time, with inverse time, is given by the expression:

b
I
k
t 


1

where
1
I
I
I
f

NOTES:
- t(s): estimated tripping time
- I
f
: fault current; given in [In] (example: 0.7In)
- I
1
, t
1
: protection L parameters set by the user, given in [In] and [s]
- , k: parameters suggested by standard IEC60255-121, which vary with the type of gradient selected (e.g. for type B
gradients: = 1 and k = 13.5)
- b: parameter included to increase the number of curves with the same slope. This parameter is automatically calcu-
lated by setting parameter t1 (required tripping time with If= 3xI1).
Protection L has 3 operating conditions established by the fault current level I
f
and by the setting of the protection itself I
1
:

Allen-Bradley LSIG-MM Specifications

General

Brand	Allen-Bradley
Model	LSIG-MM
Category	Circuit breakers
Language	English