3.1  Definition

The timing of a breaker is the time measurement of the mechanical operations in order to verify its integrity and good working order.

Mechanical operation means all operation or cycle of operation the breaker is intended to do without being connected to the power grid.
 

 3.2  Importance

It is a necessary to time each breaker, in order to have its functional signature. Incorrect operation can have disastrous consequences on the equipment or the substation personnel. Not to mention the out of service losses of revenue and the repair costs.

Timing tests are done first in the factory during the routine tests and after installation, during the commissioning tests.

They have to be done periodically in order to validate the good working order and reliability of the breaker.

Timing tests are also a powerful tool for troubleshooting faulty breakers.
 

 3.3  Description

In order to measure the operation times of a breaker, we need a device capable of detecting the instant of contact's state changing starting from the point the order was launched.

This device sends electric signals via cables connected to each contact, in the case of several contacts in series each signal has its own source to eliminate interference.

The signal has two possible states. The first is when the contact is closed, the second when the contact is open. All is recorded for consultation and analysis.

These special devices are called timing machines or circuit breaker analyzers. They are designed to generate all the needed signals and incorporate a data acquisition system.

Four steps constitute the main activities to accomplish a timing test:

1. Cable installation and connection
2. Data Acquisition
3. Data interpretation
4. Data analysis
 

 3.3.1  Installation and connection

The connection, mainly between the timing machine and the breaker, has to be done correctly taking into account certain external factors, for instance magnetic induction by nearby high voltage transmission lines.

Another connection has to take place between the timing machine and the mechanism coils responsible for launching the operation order.

Some other connections may also be required as travel transducer, pressure transducer, auxiliary contacts, etc.
 

 3.3.1.1  General rules

There are no special rules applied as long as the wanted information is obtained. But in order to avoid any unpleasant surprises, some precautions should be observed.
 

 3.3.1.2  Connection description

3.3.1.2.1 3.3.1.2.1 Connection to main contacts :

Each breaker contact has to be verified separately. For multi-contacts per phase, each contact has to have its own verification circuit.

Each verification circuit includes a voltage source that injects current on contact making; a detection circuit, to detect the current and determine if the contact is closed; two-wire shielded cable to carry the signal.

The timing machine supplies the verification circuits. Each verification circuit is called a channel.

The following figure shows en example of how the main contacts are connected to the channels:

Fig. 3.321 - Power Circuit Connections

For multiple contacts per phase, special care has to be observed to avoid the mirror effect (treated later in this article), where the data for some contacts will be corrupted by the data from other contacts.
 

 3.3.1.2.2  Connection to mechanism (command) coils:

The circuit breakers control circuit has various safeguards against malfunctions, for instance against phase discrepancy, or against pumping.

The following figure illustrates a command circuit, with some protection circuits. It is important not to bypass any of these protection circuits.

Figura 3.321b - Command Connections

A connection that bypasses the auxiliary contacts may cause the destruction of the coils.
 

 3.3.1.3  Mirror effect

No intervention on high voltage equipment should take place without proper protection to the intervening personnel first and to the intervened equipment. One of the most important protection measures is to install ground cables. Ground cables connect the line to the ground. In case of accidental energy supply to the line the current will pass through the ground cable and avoid the working personnel. Ground cables should be installed on each side of the breaker.

In the case of timing a multi-contact phase the presence of ground cables on both sides of the contacts may mask the signal of a faulty contact by the signal of a good contact, making it undetectable.

The following illustration shows this phenomenon.

Figura 3.3.13 - Mirror effect

If contact 2 stays open, while contact 1 closes, the channel 2 circuit will detect the current passing through the ground cables and will show contact 2 as being closed.

The solution would be to break the return circuit of the ground by disconnecting the breaker from the line, between the extremity of the breaker and the grounding cable next to it. By no means should the grounding cable be removed, under the risk of injury.
 

 3.3.2  Data acquisition

In addition to the signal generation, timing machines are in charge of contact transition detection and recording.

The earliest timing machines used light reflected on moving mirrors driven by the current signal coming from the contacts. The light is projected on paper film, thus creating a visible trace on the paper.

Today, in the computer age, timing machines have undergone a tremendous evolution. They use electronics and computer technology for data acquisition. Powerful software serves to analyze and conserve data for future studies. Data transmission has never been easier. Decisions can be made quickly and accurately.
 

 3.3.3  Data interpretation

Many external agents can influence greatly the collection of information. It is important to distinguish in the collected information, between the useful data and the external noise.

Good interpretation is based on three main principals:

1. Know the breaker and the surrounding environment:
Induction due to the proximity of overhead power transmission lines, or a bad cable connection could alter the collected signal.

2. Know the timing machine:
Incorrect programming or a failed circuit can cause unnoticed signal alteration as well.

3. Know the significance of the values looked for:
When timing a breaker, we are looking for certain values, such as: contact switching times, coil energizing times, etc. that can allow quick identification of a problem, and if a value seems excessive, we can look to it in time and repeat the test before taking all the cables down.
 

 3.4  Breaker's operation times

In its description, the circuit breaker is a device that conducts or interrupts currents to the circuit. This is done by mechanically joining or parting two sets of contacts. These are the basic operations of the circuit breaker and are called "CLOSE" when joining, and "TRIP" when parting the contacts.

As we mentioned before, these are not the only operations that the breaker is meant to do. In most of the cases it has to execute on demand a combination of the basic operations, called cycles. The most popular are the following:

1. "TRIP FREE", (C-O): simulates a trip on short circuit after a "CLOSE". The breaker must open instantly.
2. "RECLOSE", (O-C): simulates a fast close after short circuit trip to reestablish the current.
3. "RECLOSE-OPEN", (O-0.3s-C-O): Simulates a "RECLOSE" on short circuit. The breaker should clear the fault successfully.
4. (C-O)-15 sec-(C-O)-15-sec-(C-O): simulates a multiple close after short circuit trips in purpose of reestablishing the current, hoping that the short circuit is disappeared. This cycle is mostly used in the Medium voltage applications.

The times measured, for the different cycles starting from the coil energizing until the switching of the main contacts are called the Breaker's mechanical times of operations.
 

 3.5  General definitions

Before proceeding with the operation times, here are some of the most used terms in the breaker timing field.
 

 3.5.1  Interrupting element (or unit)

Also called arcing chamber, it is a closed volume containing the main contacts and in which current interrupting occurs.
 

 3.5.2  Pole

A pole is a part of the breaker that is installed on a line phase. The breaker is installed on three-phase line. It necessarily has three poles. Each pole includes at least one interrupting element. For high voltage levels, multi-element poles are most common.
 

 3.5.3  Main contact

These are the contacts in charge of establishing or interrupting the current flow in power circuits. They include a fixed and a moving contact.

The contact's material has to be chosen to have minimum resistance when closed, to minimize the losses by joule's effect when transiting nominal currents.

The best-suited material is silver plated copper.
 

 3.5.4  Auxiliary contact

As mentioned earlier, insertion resistors are usually used on high voltage circuit breakers, for closing, opening, or both. These resistors minimize the transition voltage before closing or after opening by engaging or disengaging auxiliary contacts in two or three steps.
 

 3.5.5  Arcing contact

For breakers, the arc can be a powerful generator of heat energy. This heat can cause fast deterioration of main contact's material. To extend life of the main contacts, breaker designers tend to separate the permanent current carriers, called "Main Contacts", from those subjected to the arc effect, and called "Arcing Contacts".

The most common material for arcing contacts are, in general, tungsten alloys, reputed to have high arc resistant quality, but are less conductive than silver-plated copper.
 

 3.5.6  Indicating contact

In order to control the breaker on low voltage side, two types of contacts were created, (a) contact and (b) contact. They are both driven by the operation of the breaker and switch states with main contacts.

They are mainly used to indicate the breaker's position and to electrically interlock between basic operations.
 

 3.5.6.1  "a" contact

It has the same state of the main contact. It closes when the main contact closes, and opens when the main contact opens.
 

 3.5.6.2  "b" contact

It has the opposite state of the main contact. It closes when the main contact opens, and opens when the main contact closes.
 

 3.6  Time reference

The basis of timing tests is to collect information in order to compare it with reference values. The comparison should be done on comparable parameters. So the collected values should follow the same rules as the reference values, and be independent of individual interpretations.

Since we are talking time, we should determine the same reference points in reading the information.

Earlier, the designers determined reference values. The users had also their reference values. This created confusion between the designer's reference values and the user's interpretation to the collected values.

In order to solve this problem, professionals tend to use the definitions as stated by international standards. The most widely used is the IEC 56 international standard.
 

 3.7  Timing definitions according to IEC 56 international standard

The IEC 56 international standard defines these times as follows:
 

 3.7.1  Opening Time (IEC 56 3.105.32)

For a circuit breaker tripped by any form of auxiliary power, the opening time is the interval of time between the instant of energizing the opening release, the circuit breaker being in the closed position, and the instant when the arcing contacts have separated in all poles.

Notes :

1. The opening time may vary significantly with the breaking current.

2. For circuit breakers with more than one interrupting unit per pole the instant when the arcing contacts have separated in all poles is determined as the instant of contact separation in the first unit of the last pole.

3. The opening time includes the operating time of any auxiliary equipment necessary to open the circuit breaker and forming an integral part of the circuit breaker.
 

 3.7.2  Closing Time (IEC 56 3.105.35)

The interval of time between energizing the closing circuit, the circuit breaker being in the open position, and the instant when the contacts touch in all poles.

Note : The closing time includes the operating time of any auxiliary equipment necessary to close the circuit breaker forming an integral part of the circuit breaker.
 

 3.7.3  Open-Close Time, O-C or Isolation time (IEC 56 3.105.38)

The interval of time between the instant when the arcing contacts have separated in all poles and the instant when the contacts touch in the first pole during a reclosing operation.
 

 3.7.4  Close-Open Time, or short-circuit time (IEC 56 3.105.42)

The interval of time between the instant when the contacts touch in the first pole during a closing operation and the instant when the arcing contacts have separated in all poles during the subsequent opening operation.

Note : Unless otherwise stated, it is assumed that the opening release incorporated in the circuit breaker is energized at the instant when the contacts touch in the first pole during closing. This represents the minimum close-open time.
 

 3.7.5  Minimum Trip Duration (IEC 56 3.105.44)

The minimum time the auxiliary power has to be applied to the opening release to ensure complete opening of the circuit breaker.
 

 3.7.6  Minimum close duration (IEC 56 3.105.45)

The minimum time the auxiliary power has to be applied to the closing device to ensure complete closing of the circuit breaker.