Insulation resistance of electrical equipment and electrical networks
The value of the insulation resistance characterizes to a greater extent the reliability of the electrical equipment and the safety of its operation.
The insulation resistance of the network depends on various factors (climatic conditions, pollution, number of connected users, etc.) and therefore even for a given network it can vary significantly. These changes can be roughly divided into two groups: normal and emergency.
Normal changes in the insulation resistance are practically not related to the appearance of defects in the insulation structure and can be caused by various climatic and temperature influences, as well as by the inconsistency of the number of connected consumers during the operation of the electrical network.
The range of normal changes in insulation resistance is a characteristic of a given network (or its part) and can be determined on the basis of static studies, taking into account the results of studies of similar networks.
Emergency changes related to the appearance of some malfunction in the insulation structure (for example, volume moistening of a temporarily non-working electric motor in a room with high humidity or mechanical damage to the insulation with subsequent moistening or contamination of the damage site, etc.). In the case of a localized reduction in insulation resistance, the active and capacitive leakage currents to the ship's hull are concentrated in one place. This process is accompanied by significant heat generation, which can lead to the destruction of the insulation, to the formation of arcing damage to the housing.
Normalization of the insulation resistance value aims to provide an opportunity to assess the state of the insulation of the network or its individual elements. For the norm of insulation resistance, the value of the range of normal changes is taken.
Insulation resistance standards for some types of electrical equipment are given in Table 1.
Section. 1. Norms of insulation resistance of electrical equipment, mOhm
Electrical equipment
Condition of electrical equipment
cold
heated
Electric machines with a rotation speed of up to 1000 rpm with power:
up to 100 kW
5
3
from 100 to 1000 kV
3
1
Transformers
5
1
Electrical panels
1
—
Control device
5
—
Power network and lighting network
1
—
Norms of insulation resistance of electrical networks depend on their branching, type and number of connected consumers.If for branch networks containing a large number of users, the insulation resistance is less than 10 kOhm, then the number of galvanically connected network elements must be reduced, for example, by using isolating transformers.