Automatic re-closing devices for breaker Yukinori Hirooka

OTOWA ELECTRIC CO.,LTD. In Japan hirooka@otowadenki.co.jp

Abstract — The automatic breaker re-closing device automatically distinguishes between mull operation of the breaker caused by a lightning surge and operation from an abnormal an overcurrent or a ground fault and automatically re-close only mull breaker operation caused by a lightning surge.

I. INTRODUCTION

Breakers are installed for the purpose of preventing fires and injuries from electrical shock by interrupting the circuit when there is an overcurrent caused by an overload or equipment failure, or an earth leakage. In Japan, installation of breakers is mandatory for prescribed loads and equipment, and breaker usage is almost 100% among customers.

Breakers are divided roughly into earth leakage circuit breakers (ELCB) and molded case circuit breakers (MCCB). When an earth leakage is detected, an ELCB amplifies the detected current through an internal electronic circuit and actuates a tripping device to trip the breaker. When an MCCB detects an overcurrent,an overcurrent tripping device actuates to trip the breaker.

In addition to operating functionally in this way, however, lightning surges, for example, can sometimes cause breakers to operate in an mull operation way. In such a case, there is no damage to the load in most cases and a normal state can be restored by re-closing.

II. MAL- OPERATION OF BREAKER

Recently, many cases of mal-operation of breaker caused by lightning surges have been reported, many of which have been verified as ELCB malfunctions.

Figure 1 shows a common power distribution system. If there is a lightning strike on a distribution line or anywhere close by, induction causes an inrush of the lightning surge into the distribution line. A very large lightning surge

current may pass through the breaker at this point, and the breaker may trip.

This occurs because the electronic circuit inside the breaker malfunctions from the effect of a magnetic field generated when the lightning surge current passes through the breaker, and the tripping device is actuated.

Fig. 1 Distribution System

In most cases of mal-operation caused by lightning surges, the load equipment is not affected, and no problem is caused by re-close the breaker.

With respect to mal-operation of breaker caused by a lightning surge, IEC 60947-2 and/or JIS C 8371 have requirements on lightning impulse withstand voltage property, and the like. Manufacturers have developed products to meet the requirements, but none can be called foolproof.

When a breaker trips, the cause of the trip needs to be checked. If the trip was caused by an abnormality in the load, the cause needs to be eliminated.

Often, however, the cause cannot be identified. Identifying the cause is particularly difficult when the trip is a malfunction.

If the breaker trips in unattended electrical equipment on top of a mountain or on a remote island, a maintenance crew has to go to the site to check the cause and for any damage to the equipment, and the loss caused by the stoppage during this time as well as the cost of sending the crew is large.

7th Asia-Pacific International Conference on Lightning, November 1-4, 2011, Chengdu, China

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2011

III. PRINCIPLE OF OPERATION

A Overview The automatic breaker re-closing device is a

device that automatically distinguishes between breaker mal-operation caused by a lightning surge and operation from an abnormal load such as an overcurrent or a ground fault and automatically re-close only breaker mal-operation caused by a lightning surge.

Fig. 2 Structure of Automatic Breaker re-closing Device

B Structure The automatic breaker re-closing device consists

mainly of the control unit, the drive unit, and the breaker unit.

The control unit recognizes whether the breaker is closed or open, and when the breaker is open, determines whether the cause is a lightning strike or an abnormality in the load.

Fig. 3 Block diagram

C Function The automatic breaker re-closing device

automatically distinguishes between operation from an abnormal load and breaker mal-operation caused by a lightning surge and automatically re-close only breaker mal-operation caused by a lightning surge. If the breaker has actuated from an abnormality in the load, there is no automatic re-closing.

Fig. 4 Flowchart

D Detection of mal- Breaker Operation A current detecting sensor is installed on the

bottom of the breaker to detect the magnetic field that is generated when lightning surge current flows into the breaker.

With leakage current, the breaker normally trips with a current of 10mA~500mA. In the case of an overcurrent, the single phase or three phase current flow is larger than a leakage current, but the magnetic field is cancelled out so that the output signal of the current detecting sensor becomes extremely low, thus making it easy to distinguish between lightning surge current and other types of current.

The sensitivity test for surge detection assumes indirect lightning strokes (8/20μs) as well as direct lightning strokes (10/350μs) and is performed using both current waveforms.

BreakerControl Unit

Drive Unit

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2011

TABLE I Detected Current Level

Cause of Trip Detected Current LevelLightning surge

current 1kA ~ 50kA

Overcurrent Cancelled outLeakage current 10mA ~ 500mA

E Automatic re-closing Mechanism There are two ways to automatically re-close the

breaker: using a motor and using a solenoid.Some switching mechanisms for the breaker

lever have only ON and OFF position, while others have ON, OFF and an intermediate Trip position.The former mechanism will accommodate both motor type and solenoid type, but the latter requires a reset operation once it is in the OFF position, so a motor mechanism is used.

IV. PERFORMANCE REQUIREMENTS

A Withstand Voltage The impulse withstand voltage to ground is 30kV

(1.2/50μs), which may be installed on primary side of Lighting Isolation Transformer.

B Lightning Surge Detection When the current sensor for detecting lightning

surges determines whether a breaker trip is caused by a lightning surge or an abnormal load, it needs to clearly distinguish between a lightning surge current and current that flows with abnormal load, such as overcurrent, leakage current, and ground current.

C Other Functions A display showing the activation count needs to

be provided so that the activation history of the automatic breaker re-closing device can be checked. Also the automatic breaker re-closing device needs to be configured so that the activation can be verified.

V. PERFORMANCE

A Withstand Voltage Since the automatic breaker re-closing device

itself does not have SPD, an SPD or a protective device needs to be installed separately in order to protect equipment from lightning surges.

The withstand voltage to ground is likewise 30kV for the automatic breaker re-closing device ,it self.

Excluding direct lightning strokes, several tens of kVs maximum have been recorded in Japan for lightning overvoltages occurring in low voltagelines. Also show 20kV peak levels in regions with frequent lightning strikes. These levels are sufficiently covered by the withstand voltage.

B Self test function Capability The automatic breaker re-closing device is

configured to allow verification of the re-closing (motor) operation, permanent cutoff operation,without actual breaker operation.

C Re-Closing time delay When the automatic breaker re-closing device

trips from a lightning surge, the delay time for re-closing can be selected from 10sec, 30sec, 1 min, 10min and 20min.

The initial setting is 10 seconds.

D Operation in a Power supply failure The various operations of the automatic breaker

re-closing device is controlled by a microcomputer. Even if the automatic breaker re-closing device trips from a lightning surge before a power supply failure, there will be automatic reset after power is restored since the detection of the lightning surge has been recorded and retained.

The activation count for the automatic breaker re-closing device before the power supply failure will also be retained.

E Reset of Permanent Cutoff made A permanent cutoff can only be released when

the breaker is closed.Reset of permanent cutoff made can only be ne

leased when the breaker is normal closed condition.This is designed so that the breaker will not

automatically close when work such as eliminating the abnormal load, restoring normal conditions and verifying safety is being performed during a permanent cutoff, or when performing regular equipment maintenance and inspection.

F Comparison with Conventional Products

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2011

With many conventional products, automatic re-close was performed a certain number of times within a certain time, regardless of the cause of breaker operation. For example, automatic re-closemight be performed up to 3 times within 5 minutes, but the 4th time would be a permanent cutoff, or there might be a permanent cutoff if the breaker was actuated within 2 seconds after resetting.

However, there was a concern that, if the circuit was interrupted owing to an abnormal load, automatically re-closing the breaker might makeany damage to equipment or damage from a fire worse.

G Maintenance Although maintenance and inspection is not

particularly required, verification of test operation is recommended once a year.

VI. PRODUCT TYPES

There are 4 types of automatic breaker re-closing device adapted to the breaker frame size – 30Aframe, 50A frame, 100A frame, and 225A frame, detail are shown in the Table 2.

TABLEMajor Product Types

FRAME 30AF 50AF 100AF 225AF

POWERSUPPLY 1 2W

1 2W1 3W3 3W

1 2W1 3W3 3W

1 2W1 3W3 3W

NUMBEROF POLES 2P 2P

3P2P3P

2P3P

VOLTAGE AC100VAC200V

AC100VAC200V

AC100VAC200V

AC100VAC200V

CURRENTRATING 15 20 30 15 20 30

40 50 60 75 100125 150 175 200

225

BREAKER MCCBELCB

MCCBELCB

MCCBELCB

MCCBELCB

VII. APPLICATION EXAMPLES

Main user 1) Mobile communication satellite stations 2) Wireless facilities for government offices 3) Broadcast station facilities 4) Emergency wireless facilities 5) Electrical facilities in plants

VIII. CONCLUSION

The automatic breaker re-closing device maintains the basic role of a breaker to “cut off power during an abnormal load condition” and provides the additional function of “automatic re-close after a mal-operation”. Installing the automatic breaker re-closing device allows rapidrestoration and cost reduction. The advantages are believed to be particularly great in the case of unattended or mountaintop facilities, since the burden of sending a maintenance crew to the site as well as the cost of labor can be reduced.

978-1-4577-1466-5/11/$26.00 ©2011 IEEE 47

2011