FUNCTION CHARACTERISTICS
77
NA10 - Manual - 04 - 2022
Cold Load Pickup - CLP
Preface
CLP feature allows selected thresholds of phase and ground overcurrent protections to be changed
or blocked for a set time in order to overcome transient overcurrents.
The trigger of the CLP feature is the logical condition of circuit breaker closed, that Pro-N relay
detect by means of two digital inputs connected to the circuit breaker auxiliary contacts 52a and 52b.
When the circuit breaker closed condition is detected, the CLP timer set in the submenu of CLP
function is initiated and, throughout the CLP set time:
• The threshold is blocked if CLP is set to ON threshold block.
• The threshold is changed to the value that is set if CLP is set to ON threshold change.
When CLP timer has elapsed, the threshold is unblocked if CLP is set to ON threshold block or the
threshold is revert back to the original value if CLP is set to ON threshold change.
Note that when the circuit breaker is open, the threshold is already blocked if CLP is set to ON
threshold block or the threshold is already changed to the value if CLP is set to ON threshold change:
this is useful in order to avoid unwanted tripping due to unblocked threshold or threshold with his
original value for cases where a delay of the circuit breaker closing happen, i.e. where the three
poles of the CB do not close at the same time or during long CB closing time.
Typical applications where the CLP feature may be useful are for overcurrent protections on feeders
where the circuit breaker closing starts air conditioning/heating loads after a long cooling time, mo-
tors or more generally momentary large loads.
The CLP may be also useful for instantaneous ground fault overcurrent protections on motors start-
ing, because it is likely that incorrect operation of the protection would occur on imbalance transient
secondary current due to asymmetric line CTs saturation.
Depending upon the magnitude and duration of the starting current, it may be necessary to block
operation of thresholds or raising his setting. Also a combination of both blocking some thresholds
and raising others may be adopted.
For each threshold the CLP function may be disabled (OFF), enabled with threshold blocking
(ON-Element blocking) or enabled with threshold change (ON-Change setting) by means the
xxCLPx Mode parameter.
The operating mode and the relative activation time concerning each threshold of the 50/51and
50N/51N elements are adjustable inside the Set\Profile A(or B)\xxx - xx \ xxx Element \Setpoints
menus.
Example: to change the first threshold of the definite time overcurrent element 50/51 within CLP
during a 0.1 s time interval:
• The ICLP> Mode parameter must be set as ON-Change setting,
• The tCLP> parameter must be adjusted to a wanted value (0.1 s) inside the Set\Profile A(or B)\
Phase overcurrent - 50/51\ I> Element \ Setpoints menu,
• The threshold within CLP parameter ICLP>def must be adjusted to a wanted value inside the Set\
Profile A(or B)\ Phase overcurrent - 50/51\ I> Element \ Definite time menu.
CB position can be acquired by means one or two binary inputs; allocation of 52a and 52b func-
tions is available inside the Set\Inputs\Binary input IN1...INx menu.
Input
t
xxRES
T0
RESET
t
xx
0T
≥ 1
I
xx
t
xxRES
Start Ixx
Trip Ixx
Start I
2ndh>
CB State
(Threshold outside CLP)
Generic protective element
Block1, Block2
T 0
t
CLPxx
&
2nd harmonic restraint enable (ON≡ Enable)
Ixx2ndh-REST
ICLPxxMode
I
CLP
xx
t
CLP
xx
TRIPPING MATRIX
(LED+RELAYS)
A
B
C
A =“1”A =“0 or OFF”
TRANSIENT THRESHOLD
STEADY STATE THRESHOLD
t
CLPxx
CB State CB CLOSED (52a=ON)
CB OPEN
(52a=OFF)
CB OPEN
(52a=OFF)
Output t
CLP
xx
t
0.1 s
TRANSIENT THRESHOLD/ TRANSIENT THRESHOLD/
BLOCK
STEADY STATE
THRESHOLD/UNBLOCK
BLOCK
A = ON - Change setting
B = OFF
C = ON - Element blocking
≥ 1
CLP Ixx
Operate time
Cold Load Pickup logic diagram - CLP
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