15 WHY's? Why is the PKV/M7 more preferable than similar instruments of other manufacturers?
A large range of instruments for HV circuit breaker control available at the market makes it difficult for a customer to select a device that is most appropriate in terms of functions and cost. .
- As compared to the standard set of the reference data, the PKV/M7 instrument provides an extended set of time, travel and speed characteristics of the drive shaft, contacts, voltages and currents. They include: time difference, chatter period, delays, rebound and over travel, different average speeds at different travel sections for different circuit breaker types, and many others.
- The PKV/M7 provides large ranges of time (up to 5.2s), speed (up to 20m/s) and travel (up to 900mm) measurements that cover all the requirements to the circuit breakers.
A smaller range of time incorporated in other instruments does not allow the circuit breaker testing in complex cycles. As to instruments with potentiometer-based displacement transducers, especially with cord-type transducers, they have the upper limit of speed. A return spring in these transducers fails to windup a cable on a drum at rapid speed changes thus increasing the measurement error. A laser displacement transducer can incidentally damage the eye by a laser beam.
- The PKV/M7 provides high precision measurements of time (±0.1ms), travel and speed characteristics that are ensured by digital transducers of linear and angle travels with the resolution capability of 0.090 and 0.5mm. Potentiometer-based transducers applied in the PKV/M7 analogues have high error (up to ±1%) even in normal conditions. At maximum displacement of 900mm the uncertainly value is as high as ± 9mm.
- The PKV/M7 has high noise immunity of measurements as digital transducers have an impulse-type low-Ohm output. Time measurement channels connected to the circuit breaker terminal via cables can be operated at high currents..
Output resistance of potentiometer-based transducers is high (up to 10 kOhm), and electromagnetic interferences of a substation create high noises that distort a friendly signal. Test currents in the PKV/M7 analogues are several times lower.
- The PKV/M7 instruments are of contact-free type, therefore, the time of operation has no impact on their metrology characteristics. As to instruments with potentiometer-based transducers, especially the cord-type ones, high accelerations create considerable mechanical loads on the elements (a spring, drum, cable, and a potentiometer), that accelerates their wear, increases the measurement error and reduces the metrology characteristics.
- The PKV/M7 has been adapted to a large number of HV circuit breakers, such as ABB, AREVA, ALSTOM, Siemens, and many others. The instrument is continuously adapted to new emerging circuit breakers of other manufacturers. The PKV/M7 is currently being adapted to vacuum circuit breakers that would allow measurement of both time and speed characteristics. Experience has shown their practicality though, according to passports of vacuum circuit breakers, the speed measurements are not mandatory. But circuit breakers tend to break with time, no matter what their manufactures warrant. According to the existing codes, HV circuit breaker repair shall be followed by test of speed characteristics using a certified instrument.
Manuals for the PKV/M7 analogues do not even mention the ability to adapt to different circuit breakers.
- The PKV/M7 allows measurement of time and average speed on the travel section of vacuum circuit breakers already now, subject to the use of the built-in contact transducers. For that purpose the contact transducer is connected to the D channel input via a standard cable available with the instrument kit.
- Together with the PKV/M7 a customer procures a required set of fasteners for all the types and brands of circuit breakers available with the customer. Fasteners and accessories are continuously developed within the framework of the program of the instrument adaptation to new circuit breakers emerging in Russia and in the CIS countries.
The review shows that analogue instruments, as a rule, have no such accessories. And the customers have to develop and manufacture such accessories themselves.
- The PKV/M7 integrates a special Shuffle Bar-Angle Gage mode that facilitates adjustment of the initial angle and travel of circuit breakers during their repair.
- The PKV/M7 allows construction of the connecting rod or shaft travel graphs of "speed vs travel" or "travel vs time" dependences. The type of the graph is determined by condition of all the elements (levers, springs, operating rods, axes, connecting rods, dampers, etc.) in the kinematic chain of a mechanism controlling the circuit breaker contacts opening-closing. Failure in any link of the chain (clearance increase, spring slackening, higher friction, damper fault, etc.) immediately changes the graph view as compared with the graph of a properly operating circuit breaker. The SKB EP Company has developed a method for graphs analysis whose application allows early diagnosis of the circuit breaker state.
- The PKV/M7 switchboard allows circuit breaker control in simple and complex switchover cycles on the AC/DC currents of electric magnets of up to 10A by specifying the required time of open/close impulses, pauses and tripping delays..
- The PKV/M7 is easy to use as all the stages of its operation are very well though over:
- During cables being connected to the circuit breaker terminals, there is no need to think about ends polarity; the instrument is operable at any poles connection;
- There is no need to guess the correct installation of transducers. Detailed guidelines with figures and photos facilitate that procedure;
- You may not be afraid of mistakes during control power supply to electric magnets. High-speed switchboard protection will trip this circuit in 3 ms should a short circuit occur in it;
- Current clips facilitate measurement of currents in the electric magnets and solenoids. Upon order the instrument is completed with clips for specified currents;
- Electromagnet currents graphs allow us to make judgments on the operating voltage, on the condition of block contacts control, etc. An appendix to the PKV/M7 User Manual gives guidelines on determining these parameters using the graph obtained;
- It also describes a method for early non-destructive diagnosis of the circuit breaker mechanism that is based on speed characteristics;
- A network adapter has outputs for alternating (from the mains) and direct (from an internal rectifier) currents of up to 32A and a universal connection of the input lead to a socket (via protected plugs); to clamping screws (via insulated tags); to any conductor elements up to 20mm thick (via insulated 'crocodile' clips). A free end of the earthing wire is furnished with a mini G-clamp. This adapter eliminates problems of mains connection at a substation and ensures electric safety;
- Results of measurements are stored in the self-powered memory and can be output to a display, downloaded to a USB-card or to a PC. The latter option is rather valuable as it allows comparison of the measured data to the reference data base available in the computer.