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Technical characteristics of protective and disconnecting devices for mobile and portable current collectors. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Electrician's Handbook
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Protective disconnect devices designed to protect against electric shock to people working with electrical installations of alternating current. Currently, a large number of protective shutdown schemes have been developed. Technical characteristics of some devices used in networks with grounded neutral are given in Table. 12.
Table 12. Technical characteristics of protective and disconnecting devices for mobile and portable current collectors
In networks with grounded and isolated neutral, it is possible to use ZOUP-25 protective and disconnecting devices, designed for a consumer current of up to 25 A at a voltage of 380 V; protection setting - 10 mA, shutdown time - 0,05 s, weight - 4,5 kg. When working with power tools of single-phase current with a total power of 0,5 kW at 220 V, ZOU-1 protective shutdown devices are used. For electric welding, the device of the USNT-4 type is the most promising. When connecting a three-phase motor to a single-phase network using capacitors, it must be taken into account that the rated voltage of capacitors of the KBG-MN and BGT types is given for their operation at direct current. When they work on alternating current, the value of the allowable voltage should not exceed the values \u13b\uXNUMXbspecified in Table. XNUMX.
Table 13. Permissible stress values
If a three-phase motor is connected to a single-phase network according to the scheme (see Fig. 98, b), then the starting torque will be almost half that when switched on according to another scheme (see Fig. 98, a). To change the direction of movement of the rotor (reversal) of an electric motor connected according to the scheme (see Fig. 98, b), it is necessary to swap the conclusions C2 and C5 of the starting winding. Before reversing, the motor must be disconnected from the mains.
The value of starting active resistances is determined according to the table. 14 depending on the power of the electric motor in three-phase mode.
Table 14 Starting resistance values
Author: Korshevr N.G.
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