Pin Insulator:- Pin insulators are commonly used on rural and urban primary distribution lines. These can be used up to 33 kV. Pin insulators can be of a single piece or multipiece. The pin type of insulators is uneconomical beyond 33 kV operating voltage. Also, the replacement of these insulators is expensive. For these reasons for insulating overhead lines against higher voltages, suspension insulators are used.
Strain Insulator:- The strain insulators are exactly identical in shape with the suspension insulators. These are used to take the tension of the conductors at line terminals, at angle towers, at road crossings, and at the junction of overhead lines with cables. These insulators are, therefore, known as tension or strain insulators. For low voltage lines (less than 11 kV), shackle insulators are used as strain insulators.
In terms of slip, the actual speed of the motor (N) can be expressed as
N = Ns(1 − s)
At start, the motor is at rest and hence its speed N is zero.
s = 1 ( start)
This is the maximum value of slip s possible for the induction motor which occurs at start. While s = 0 gives us N = N. which is not possible for an induction motor. So slip of the induction motor cannot be zero under any circumstances.
Practically motor operates in the slip range of 0.01 to 0.05 i.e. 1 % to 5 %. The slip corresponding to the full load speed of the motor is called full load slip.
Indian Electricity Rules specify that the maximum load on a power sub-circuit should not exceed 3000 watts and the number of outlets should be limited to two.
The difference in level between points of supports and the lowest point on the conductor is called sag.
When the conductor is suspended between two supports at some level, it takes the shape of a catenary. However, if the sag is very small compared with the span, then the sag-span curve is like a parabola.
The tension at any point on the conductor acts tangentially. Thus tension To at the lowest point O acts horizontally.
Magnetic Field Strength (H) gives the quantitative measure of strongness or weakness of the magnetic field.
H = B/μo
B = Magnetic Flux Density
μo = Vacuum Permeability
The magnetic Field strength at the center of circular loop carrying current I is given by
B = μoI/2r
B/μo = I/2r
H = I/2r At/m
Where r = Radius
No of disc required for 11 kV transmission line = 1 disc
Since the transmission line is 3-phase, therefore, the number of discs required for a single-pole will be 3.
Total no. of poles = 80
No of disc = 3 × 80 = 240