Cold Load Pickup

The cold load pickup function is used to prevent the recloser from incorrectly operating caused by the restoration of load supply or the cold load current of load side. ETR300-R provides “CLPU-Type 1” to prevent the recloser from operating wrong by instantaneous inrush current occurring by the closing of device on a power line and “CLPU-Type 2” to prevent protection elements from operating wrong by the cold load current caused by applying voltage to a transformer, a reactor or a long-distance line.

7.1.12.1. Cold Load Pickup – Type 1

The settings of “CLPU-Type 1” are separated and set respectively for phase, ground, SEF or negative phase over current element.

In the state of the function to restrain the inrush current activated, the overcurrent protection element will be operated under settings of “CLPU-Type 1” function at the restoration of load supply.

NOTE:

According to setting of “Make use ‘I’”, the condition to decide the restoration of load supply will be changed. If “YES” is set, the decision is made when the load current becomes over 2A.

If “NO” is set, the decision is made when a recloser is closed (51A) by local or remote control.

When a distributed system is closed after long-time outage, the inrush current over overcurrent pickup level may occur. At occurrence of the cold load pickup, ETR300-R increases the pickup level of overcurrent element during a certain period of time, the Fast overcurrent protection element is not operated and the Delay overcurrent protection element is always operated regardless of the cold load pickup function. (The High Current Trip and High Current Lockout are always operated regardless of the cold load pickup function)

If a fault occurs on distributed system, an overcurrent protection element is operated by the cold load pickup function and a recloser becomes lockout after oneshot trip regardless of total number of shots.

A power is lost and then after certain outage time, the algorithm of cold load pickup function is applied at the restoration of load supply. If the “Make use ‘1’” is set to be “YES”, the algorithm is applied when a load current becomes 0 and then it is restored after certain outage time. If “NO” is set, the algorithm is applied when a recloser is opened and then after certain outage time, the

recloser is closed manually. If the fault current over the cold load pickup level occurs, the protection element by the cold load pickup function is operated immediately.

If the power loss (opening or load current loss) is sustained for a long time more than certain outage time, the pickup current of time overcurrent element is changed to be the setting value of the cold load pickup current. After the restoration of load supply (manually closing or restoration of load current), protection functions are normally operated when the Restore minimum time (RMT) is expired.

Figure 7-5. The Cold Load Pickup Characteristic

The cold load pickup function is operated according to the following rules.

The setting to use the cold load pickup function is set to be ON (set to TRIP or TR&AR), the cold load pickup level is preset and then the cold load pickup function is activated at manual close or restoration of load current.

If the level of over current occurring at the restoration of load supply is over the cold load pickup current, the Lockout is done by protection function after oneshot trip (Refer the Inrush Current 1 in

“Figure 7-6. The Restore Minimum Time Characteristic”).

If the over current is below cold load pickup current and overcurrent pickup current, protection functions are not operated during a period of Restore minimum Time (RMT), (Refer the Inrush

Overcurrent Pickup Level

Cold load Pickup Level

Trip Area

Time

Current

Delay Curve Non Trip Area

Current 2 in “Figure 7-6. The Restore Minimum Time Characteristic”). After RMT, the protection functions are operated. However, if the over current is dropped below overcurrent pickup current during the RMT, the cold load pickup function is reset after reset time (Refer the Inrush Current 3 in “Figure 7-6. The Restore Minimum Time Characteristic”).

Figure 7-6. The Restore Minimum Time Characteristic

If high current trip and high current lockout functions are activated and the fault current is higher than the current setting of High current trip and high current lockout, the high current trip and high current lockout functions will be operated prior to the cold load pickup function.

Time Current

Overcurrent CLPU

Pickup Level Pickup Level

Trip Outage time Restore Minimum Time

Trip

Inrush current 1

Inrush current 2

Inrush current 3

7.1.12.2. Cold Load Pickup – Type 2

In the state of cold load, this type is used to restrain the operation of protection functions to over current occurring by change of load (the close of a switch on long-distance line, incoming heavy load etc.). This function to restrain protection functions rises or drops the pickup level of time overcurrent element during certain time (E-CLP time) defined by a user.

Over Current Pickup Level Step Up

At power loss (a recloser is opened or a load current is 0A), the current of Over Current Pickup is risen as follows.

⎟⎟⎠

⎜⎜ ⎞

⎝

⎛ × − −

+ −

= 1 ( ' 1)

' E CLPMulti

Time CLP E

Time Supply Without

Multi Load Cold l Operationa

As example, when E-CLP Multi and E-CLT Time are set to be 3.0 and 60min respectively, over 30 min after power loss, the applied cold load multiple is 2. If the minimum working currentis set to be 200A, the current of Over Current Pickup becomes 400A, twice as much as the minimum working current. In addition, after 60 min, the cold load multiple is fixed to be 3.

Over Current Pickup Level Step Down

If power is restored (manual closed or restoration of load current (over 2A)), the current of Over Current Pickup is dropped with the same speed when rising until the cold load multiple becomes 1.

When E-CLP Multi and E-CLP Time are set to be 3.0 and 60 min respectively, the graph of the cold load multiple in “Figure 7-7. Cold Load Multipilier” is shown as follows.

NOTE:

The risen level of overcurrent pickup by multiple of cold load is the pickup level to operate overcurrent protection element. The standard current level of TC curve is a minimum working current.

Figure 7-7. Cold Load Multipilier

7.1.12.3. Cold Load Pickup Setup

The Cold Load Pickup feature in the following settings should be enabled.