CAT Advanced series provides an easy selection of different operational modes:
Open (O) ; Close (C) ; Reclose (O-0,3s-C) ; Trip free (CO) ; O-0,3s-CO ; Open-Close (O-C) ; Close-Open (C-O) ; Open-Close-Open (O-C-O) ; First trip (O)
Multiple operations, such as Open-Close and Open-Close-Open, can be initiated by using a predefined delay time or by sensing a breaker’s contact position.
The circuit breaker operation can be initiated in different ways (for instance from a control room, by a local switch or externally by a testing device) depending on a testing condition. The several time measurement triggers are available to record a measurement in a various:
The auxiliary inputs are used to monitor dry and wet auxiliary contacts. The six coil control analog channels can measure and record coil currents simultaneously (OPEN and CLOSE), up to 35 A AC/DC.
The additional six voltage analog channels have four selectable voltage ranges available (±1 V, ±5 V, ±60 V and ±300 V AC/DC). They are used to monitor:
Three transducer channels provide measuring displacement of the circuit breaker moving parts, contact wipe, over-travel, rebound, damping time and an average velocity. Either an analog or a digital transducer can be connected to these universal channels.
1 - Mains power supply input 90 – 264 V AC;50 Hz – 60 Hz
2 - PC communication USB interface
3 - Flash drive. Used for a direct download of test results on a USB memory stick
4 - Thermal printer (optional). (Built-in 112 mm (4.4 inch) wide) Graphic and numeric printout of contact and travel wave form
5 - Main contacts inputs. Used for timing of the main and pre-insertion resistor contacts, and for the resistance measurement of the pre-insertion resistors
6 - Analog channels inputs Used for a voltage measurement of an analog signal that may be relevant.
7 - Current clamps voltage supply 24 V voltage output for current clamps
8 - Coil supply input. Separated voltage supply inputs for open and close coil control
9 - Motion transducer inputs. Intended for measuring displacement of circuit breaker’s moving parts
10 - Auxiliary inputs. Used for timing measurement of dry or wet auxiliary contacts
11 - READY button Prepares the instrument for the start of the test
12 - Coil control outputs & external trigger input. Used for operating the circuit breaker OPEN and CLOSE coil or external trigger feature
13 - Breaker state indicator. Indicates CLOSE or OPEN breaker position
14 - Micro Ohmmeter. (built-in micro ohmmeter – up to 500 A DC) for static and dynamic contact resistance measurement (not available with CAT64A and CAT124A)
15 - Alphanumeric keypad. Used for entering breaker data, test data and control functions
16 - LCD display. 20 characters by 4 Lines; LCD display with backlight, viewable in bright sunlight
1 - Mains power supply input 90 – 264 V AC;50 Hz – 60 Hz
Timing measurement of the mechanical operations is one of the most important tests to determine real condition of the circuit breaker. Timing measurement tests fulfill all the requirements defined by IEC 62271-100 and IEEE C37.09.
In three-phase systems, not only the contacts in a single pole have to operate simultaneously, but all poles must also operate at the same time. All contacts must be synchronized, within a certain tolerance limit.
Synchronization between the circuit breaker poles during opening shall not exceed 1/6 of the rated frequency cycle (3,33 ms at 50 Hz; 2,78 ms at 60 Hz) and during closing shall not exceed 1/4 of the rated frequency cycle, as well (5,0 ms at 50 Hz; 4,17 ms at 60 Hz).
Simultaneous measurements within a single phase are important in situations where a number of contacts are connected in series.
The maximum difference between the instants of contact separation within series connected interrupter units shall not exceed 1/8 of a cycle of rated frequency (2,50 ms at 50 Hz; 2,08 ms at 60 Hz). Maximum difference between the instants of contacts touching within series connected interrupter units shall not exceed a 1/6 of a cycle of rated frequency (3,33 ms at 50 Hz; 2,78 ms at 60 Hz).
Auxiliary contacts are mechanically driven by the operating mechanism and are used for control and indication of main contacts state. There are no general requirements, related to timing measurement of auxiliary contacts, described in IEC® and IEEE® standards. Anyway, in order to assess condition of high-voltage circuit breakers, it is important to check their operation.
Type "a" contact follows circuit breaker main contact position and must close/open ahead of the closing/opening of the main contact. Type "a" contact is connected in series with the open coil and interrupts the open coil circuit when the circuit breaker opens.
The "b" contact must open/close when the operating mechanism has released its stored energy in order to close/open the breaker. Type "b" contact is connected in series with the closing coil, interrupting the closing coil circuit when the circuit breaker closes.
Both Sides Grounded
Utilities and service companies increase their emphasis and demands on the safety regulations. In all substations grounding on both sides of the circuit breaker contacts is the best way to provide safety. These safety grounds eliminate any static discharge in the circuit breaker contact and conduct any line power close to the circuit breaker while the personnel are working. These earth grounds present a short-circuit condition to the traditional test equipment, and therefore the circuit breaker always looks to be in the closed state. In practice, it is necessary to remove at least one of the safety grounds from the circuit breaker prior to testing, and to reinstall the ground(s) after testing is complete. This procedure is not desirable as it introduces a possibility that the ground may not be reconnected after the test, presenting a safety hazard. Both Sides Grounded (BSG) feature enables safe and fast testing in high voltage substations, without removing the safety ground connections on both sides of the circuit breaker. No additional modules or remote boxes are required. Each main contacts timing channel is able to detect main contacts state in case when both terminals are grounded.
Motion measurement of the high voltage circuit breakers’ contact system is of crucial importance for assessing a condition of the test object. The three motion transducer channels can acquire data from 3 linear or rotary motion transducers. Each channel can be configured for either an analog or a digital transducer.
Due to universal transducer channels design, a user is able to connect a variety of motion transducers available on the market.
Performance values such as stroke, over-travel, rebound, contact wipe are obtained as a result of the measurement. These values can be compared to the manufacturer’s reference data and data acquired from previous measurements. This provides indications about potential wear of the breaker.
Average velocity is calculated between the two points on the motion curve. The upper point is defined as a distance in length or time elapsed from the breaker’s closed position, or contact-separation point. The lower point is determined based on the upper point. It can either be a distance below the upper point or a time before the upper point. Up to 5 zones for average velocity calculation can be selected.
Digital rotary transducer mounted on ABB LTB 245 kV SF6 circuit breaker User is usually allowed to mount transducers on accessible parts of the circuit breaker’s mechanical linkage. Beside this, instrument often records rotary motion, even it is known the main contacts motion is linear. As a result, motion results obtained do not represent real movement of the main contacts, but just linear or nonlinear interpretation of the main contacts moving parts displacement. Amperis-Win software provides transfer function feature which allows user to define linear or non-linear parameters in order to obtain actual displacement values of the main contact moving parts.
Coil current measurement
The IEC 62271-100 standard states that it is desirable to record the coil currents waveform, since it provides information about coils’ condition (e.g. increased friction of the plungers, burned insulation, short-circuited part of the winding), the latch for release of the operating mechanism (e.g. increased friction) and the operating mechanism (e.g. if there is reduced operating mechanism speed that can be seen based on the opening time of auxiliary contacts).
When the opening or closing command is initiated, the coil is energized (point 1) and the current rises causing a magnetic field to apply a force on the iron plunger. When the force on the plunger exceeds the retaining force the plunger begins to move (point 2). The motion of the iron plunger induces an EMF in the coil, effectively reducing the current.
The combined mass of the plunger and the latch continue to move at a reduced velocity causing a further reduction in the coil current (points 2 to 3) until it hits a buffer bringing it to a rest (point 3). If the current values at points 2 and 3 are higher than specified and the time at point 3 is longer than specified, it may indicate a friction of the plunger and latch. With the plunger at rest, the current increases to the saturation level (DC current which is proportional to the coil resistance, point 4). If the current value from point 4 to point 5 deviates from specific it may indicate a burned insulation or short-circuited part of the winding of coil. Meanwhile, the latch unlocks operating mechanism, releasing the stored energy to open the main breaker contacts. Typically, after a short delay the auxiliary contacts open, disconnecting the opening coil from the control voltage (point 5). As the coil is de-energized the current drops quickly to zero in accordance with the coil inductance (point 6). Longer time than specified at points 5 and 6 may indicate auxiliary contact malfunction or insufficient driving energy of the operating mechanism.
Static resistance measurement
The built-in micro ohmmeter generates up to 500A true DC ripple free current with an automatically regulated test ramps. The resistance measurement is using the well-known Kelvin’s four point’s method.
The DC current is generated through the closed circuit breaker contacts. Voltage drop is measured between terminals of the circuit breakers. The resistance is calculated using the Ohm’s law R=U/I.
High – Precision module (built-in)
The high-precision module is newly developed built-in addition to 500 A micro ohmmeter available in CAT36 model. It provides an increased precision and offers a highly accurate contact resistance measurement in the range from 1 μΩ to 30 μΩ, with 0,01 μΩ resolution. CAT36 with the built-in High Precision Module may be used for applications on very small resistance measurements of non-inductive test objects. This requirement is usually met at resistance inspections of generator circuit breakers, welding joints, GIS testing, etc.
DRM (Dynamic Resistance Measurement)
The built-in micro ohmmeter can also be used for the DRM. DRM test is performed by injecting a current through the breaker contact and simultaneously monitoring the voltage drop across the breaker contact as well as the current flow during the breaker operation. The DRM test requires the circuit breaker analyzer with a high resolution measurement.
The resistance curve, as a function of a contact travel can be used to reveal potential problems related to the arcing contact condition. The injected current value should be as high as possible but no less than 100 A, to provide a reliable voltage drop reading, thus allowing an easier detection of the arcing contact.
CAT36, CAT66 and CAT126 models incorporate the most powerful micro ohmmeter generating up to 500 A.
First trip test
“First trip” analysis is important to determine a condition of the coil operating mechanism. Circuit breaker spends most of its lifetime conducting a current without any operation. Once the protective relay detects a problem, the circuit breaker, that was idle for maybe a year or longer, has to operate as fast as possible. However, if the circuit breaker has not been operated for a long time, the friction of the trip latch release mechanism may increase. Information about the latch friction, open circuit contacts, insufficient spring tension, can be learned from the coil current waveform recorded during the “First trip” test.
Since the breaker is in service, the conventional way of off-line timing measurement with timing cables across the interrupter cannot be used. Instead of main contact timing cables, three current probes are used. These current probes show current flowing through the secondary side of the current transformer for each phase. The instant when the current stops flowing, reveals the breaker open time.
Acquisition and Analysis Amperis-Win software provides acquisition and analysis of the test results, as well as control of all the CAT Advanced series functions from a PC. It supports measurements process and step by step guidance through the entire test procedure, providing faster, easier and safer testing. Graphical presentation Graphical presentation of a variety of measurements and timing test results uses cursors and powerful zoom functions for detailed analysis. Colors, grids, scales and positioning of the test data are all controlled by the user. Amperis-Win supports automatic unit conversion (e.g.: cycles to seconds or mm to inches). The test records can be exported in .dwc file format for further analysis.