1, for disk mounted measurement of voltage, current can be used voltmeter, ammeter, respectively, and voltage transformer, current transformer connection measurement. Voltage transformer is divided into two categories according to the principle of electromagnetic induction and capacitive voltage divider, electromagnetic induction is used for 220kV and the following voltage levels. Capacitive voltage divider is generally used in power systems above 110KV, 330 ~ 765kV ultra-high voltage power system applications. Voltage transformer according to the use of measurement and protection are divided into two categories. The main technical requirements of the former is to ensure the necessary accuracy; the latter may have some special requirements, such as the requirement of a third winding, the core has a zero sequence flux. Electromagnetic induction voltage transformer with the same principle of operation and transformer, the basic structure is also the core and the original and secondary windings. Characterized by a small and relatively constant capacity, close to no-load state during normal operation. Voltage transformer itself is very small impedance, once the vice side of the short circuit occurs, the current will grow dramatically and burn the coil. For this reason, the original side of the voltage transformer connected to the fuse, the vice side of the reliable grounding, so as to avoid the original, vice insulation damage, the vice side of the high potential to ground and cause personal and equipment accidents. Measurement of voltage transformers are generally made into a single-phase double coil structure, the primary voltage for the measured voltage (such as line voltage of the power system), can be used in a single-phase, but also can be used in two units connected to the V-V shape for three-phase use. Current transformer using the transformer primary and secondary currents proportional to the characteristics of made. Its principle of operation, the equivalent circuit is also the same as the general transformer, only its primary winding in series in the measured circuit, and the number of turns is very small; secondary winding connected to the ammeter, relay current coils and other low-impedance loads, approximate short-circuit. The primary current (i.e., the current to be measured) and the secondary current depend on the load of the circuit under test, and have nothing to do with the load on the secondary side of the current transformer. As the secondary side is close to a short circuit, so the primary and secondary voltage U1 and Uc2 are very small, the excitation current I0 is also very small. 2, for disk mounted frequency measurement can be used disk mounted analog or digital frequency meter. Analog measurement principle
1) Direct method
2) Comparison method
Digital measurement principle
1) Gated counting method of measurement principle
2) The basic composition of the universal counter <BR> 3, insulation resistance measurement can be used megohmmeter, also called a shaking table. Its working principle is that the DC power supply generally by the internal hand-cranked generator supply, electric megohmmeter DC power supply is used to make the battery transistor oscillator to produce AC voltage, the transformer step-up and doubling rectifier output DC high-voltage **** to. When using megohmmeter shake test insulation resistance of electrical equipment, must pay attention to the "L" and "E" end can not be connected to the reverse, the correct connection is: "L" line end knob connected to the measured equipment conductor, "E" ground, "L" line end knob connected to the measured equipment conductor, "E" ground, "L" line end knob connected to the measured equipment conductor. "E" ground end knob to ground the equipment shell, "G" shielded end of the insulated part of the device under test. (1) Measurement must be measured before the equipment power cut off, and short-circuit discharge to ground, never allow the equipment charged for measurement to ensure personal and equipment safety. (2) For equipment that may induce high voltage, this possibility must be eliminated before measurement. (3) The surface of the measured object should be clean to reduce the contact resistance and ensure the correctness of the measurement results. (4) Measurement should be checked before the megohmmeter is in normal working condition, mainly check its "0" and "∞" two points. That is, shake the handle, so that the motor to reach the rated speed, megohmmeter in the short-circuit should be pointed at the "0" position, open-circuit should be pointed at the "∞" position. (5) megohmmeter should be placed in a stable, solid place, and away from large external current conductors and external magnetic fields. 4, grounding resistance measurement can be used grounding resistance meter. Its working principle and megohmmeter is basically the same. Three-point method can be used to measure the grounding resistance of the equipment. Grounding probe pin 2, wire: 5 meters a (for the grounding pole), 20 meters a (for the potential probe pin), 40 meters a (for the current probe pin). 5, if the site for measurement, respectively, can be used clamp meter, multimeter, portable frequency meter, multi-function tester and other intelligent measuring instruments for on-site measurement. At present, such products, whether imported or domestic are more, and the function is also very complete.