Philips Electromagnetic Lamp manual Maximum coil temperature tw and ΔT, 111

5

1.5 Ballast specification and marking

- rated voltage, capacitance and tolerance of separate series capacitor.

In the documentation can be found:

-weight,

-overall and mounting dimensions,

-power factor (λ, P.F. or cos ϕ),

-compensating capacitor value and voltage for λ = 0.85 or 0.9,

-mains current nominal and during running-up, both with and without power factor correction,

-watt losses (normally in cold condition),

-description of version, e.g. open impregnated,‘plastic’ encapsulated, potted or compound filled.

This information suffices to find the right ballast for a certain application.Additional information can be obtained on request or can be found in special application notes. Philips ballasts are designed for use with IEC standardised fluorescent lamps.

1 6 Maximum coil temperature tw and ΔT

Fig. 105. The nominal life of choke coils in relation to the permitted rated maximum operating temperature of a ballast winding tw, dependent on insulation material:

a)class A: tw 105 ºC,

b)class E: tw 120 ºC,

c)class F or H: tw 130 ºC .

A ballast, like most electrical components, generates heat due to its ohmic resistance and magnetic losses. Each component has a maximum temperature which may not be exceeded. For ballasts it is the temperature of the choke coil during operation that is important. The maximum permissible coil temperature tw is marked on the ballast. Coil insulating material, in combination with lacquer, encapsulation material etc., is so chosen that below that temperature the life specified for the ballast is achieved.A tw value of 130 ºC is usual nowadays with a coil insulating class F (150 ºC) or class H (180 ºC). Under standard conditions, an average ballast life of ten years may be expected in the case of continuous operation at a coil temperature of tw ºC.As a rule of thumb, a 10 ºC temperature rise above the tw value will halve its expected life (see Fig. 105). If, for instance, the operating temperature is 20 ºC above the tw value, one may expect a ballast life of 2.5 years of continuous operation. If no tw value is marked on the ballast, a maximum of 105 ºC is assumed for the coil temperature. As the ballast normally does not function continuously, the actual life of the ballast can be very long. It also takes some hours before the thermal equilibrium is reached in the ballast, which again increases the practical ballast lifetime.

To verify the tw marking, accelerated lifetime tests are done at ballast temperatures above 200 ºC for 30 or 60 days.

temp. (°C)

250
200		(c)
		(b)
150		(a)
100
0,1	1,0	10

t (years)

111