Dielectric strength test is an important part of electrical product safety. It is by applying a voltage higher than its rated value to the equipment and maintaining it for a certain period of time to determine whether the insulating material and space distance of the equipment meet the requirements, i.e., it is a means of utilizing high voltage to check whether there are any weaknesses and defects in the electrical insulation structure.
Oxygen chamber national standards, oxygen chamber current input and the chamber should be able to withstand 50Hz, 1500V sine wave test voltage, lasted 1 minute, no flashover and breakdown phenomenon. This requirement is quoted from GB9706.1 Medical Electrical Equipment Part I: General Requirements for Safety. And all utility grid power supply electrical equipment and household appliances are required to input power lines and chassis to withstand 1000V plus twice the working voltage and not less than 1500V AC voltage withstand test.
If the conductor insulation is poor, line condensation moisture, aging or mechanical damage, when the external circuit high-voltage penetration will occur when the flashover to the breakdown, which leads to electrical sparks and chassis charged.
The Practical Electrician's Handbook recommends that power distribution devices, power wiring and secondary circuits below 1000V (operation, protection of electrical equipment. Measurement, signaling circuits and their instrumentation) whose voltage withstand test is 1000 V. The voltage withstand of the distribution device is the test relative to the ground, can also be replaced by a megohmmeter of 2500 V. The voltage withstand of the distribution device is the test relative to the ground. Secondary circuits with operating voltages lower than 48V are not tested for AC withstand voltage. Electrical insulation diagram is the basis of dielectric strength test, the use of insulation diagrams, can be simple and clear expression of the insulation between the parts of the relationship between the fit, suitable for the exchange of personnel at all levels. Only after familiarizing yourself with the structure of the product and the purpose of each component can you design a safe and economical insulation fit. In the combination between the following parts, should consider its isolation requirements:
Electrified parts; separated parts; grounding system; accessible enclosure; signaling circuits; patient circuits;
GB9706.1 standard gives the requirements between the various components, such as the isolation between the electrically charged part and has been protected from the grounding (A-a1), this insulation is the basic insulation (due to the failure of the basic insulation in a single fault) case, the basic insulation failure, the protection of the wiring system can produce a great instantaneous current, the fuse burns out, so as to realize the safety protection); charged parts and unprotected grounding between the shell parts (A-a2), this insulation is a double insulation or reinforced insulation (due to the shell does not have a protective grounding, according to the principle of double, even in the event of a single fault, the shell parts can not be electrically charged); other components Requirements between, will not be repeated here, the standard are described in detail. For the development of electrical insulation diagrams, the following steps can generally be followed.
a) Confirmation of equipment circuit diagrams;
b) Determine the object of protection;
c) Determine the insulation path;
d) Determine the type of insulation;
e) Determine the value of the dielectric strength test voltage;
f) Define creepage distances and electrical clearances;
g) Formulation of the table, which constitutes a portion of the insulation diagram. part of the insulation diagram.
Test voltage
The voltage required for the dielectric strength test depends mainly on the selection of the reference voltage and the determination of the insulation category. Reference voltage selection between the insulation layer, is the equipment in normal use, equipment to apply the rated supply voltage in the insulation system can appear in the maximum voltage, in the selection of the main two cases.
(1) selected insulation maximum voltage value of one end: in normal use when the equipment is applied to the rated supply voltage or the manufacturer of the voltage of the higher of the two voltages, the equipment insulation may withstand the voltage.
(2) select the arithmetic sum of the maximum voltage between any two points: for insulation between two isolated parts or between an isolated part and a grounded part, the reference voltage (U) is equal to the arithmetic sum of the maximum voltage between any two points of the two parts. Dielectric strength test is to check the insulation structure and insulating materials in a certain electric field strength whether the insulation breakdown occurs, and in the implementation of the specific test, the action of the overcurrent breaking device will become the basis for judgment, the action current is the leakage current.