01 Calculate number of channels and heat sinks

Channel capacity

4 types of channels are available.

Each successive type multiplies the capacity of the ELC.

phase angle triac
zero crossing triacs
SSRs
high power switch

1. Triac phase angle/variable channel

Maximum 3. For 3ph systems: 1 per phase

Typically, one triac channel will switch 8 ampere. 12 or 16 ampere is also possible with adequate cooling.

The triac BTA41 can switch up to 40A. But in order to reach this, very good cooling is necessary, which is costly.

Also most dump loads are not that big.

2. Triac zero crossing/static channel

Maximum 12. For 3ph systems: 4 per phase

See above.

The dump load on one static channel must be equal or smaller than on the variable channel.

3. SSR channel

Maximum 21 or 7 per phase

The SSR carlo gavazzi RA 4850-D12 can switch 50A, but I typically operate it at 32 A.

The surface temperature of the SSR can be higher than the triac, therefore normal cooling measures are acceptable.

control voltage from the hydrocontrol: 5V DC -> the SSR input must accept 5V DC.

The above SSR accepts 4.5V - 32V DC

The dump load on one SSR must be equal or smaller than all static triac dump loads on one phase.

4. High power switches

e.g. 150A per channel

3 solutions:

- high power zero crossing SSRs (recommended solution)

- mechanical high power contactors

- discrete solid state thyristor SCR modules with driver electronics

SSR advantage: easy handling, precise zero crossing switching

disadvantage: cooling necessary

contactor advantage: no extra electronics and cooling needed, high voltage proof

disadvantage: unprecise timing. for 1 or 2 periods, the full load will be on

potential disadvantage: limited number of switching actions during the lifetime.

configure the dump load size in such a way,

that switching action are limited to a few per day.

thyristors advantage: precise timing, phase angle possible

disadvantage: extra driver electronics and cooling needed

price: all in all, comparable.

The dump load on one high power switch must be equal or smaller than all SSR dump loads on one phase.

Example calculation:

My ELC shall have 100kW at 230V

minimum Ampere I_min

I_min = P/U = 100kW/230V = 435 Ampere = 145 A per phase

1. phase angle triac 8 A

2. 4 x static triac = 4 x 8A = 32 A

3. 5 x SSR = 5 x 24 A = 120A

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Total 160A per phase or 480 A total

Result: 5 triacs and 5 SSRs per phase, or 15 Triacs and 15 SSRs in total

Remark

If you max out the ampere ratings of the triacs and the SSRs, you could do with half the channels.

Advantage: Less wiring, less components

Disadvantage: components need to be cooled better, no heat/current safety margin, if one component fails, a lot of dump loads are inactive.

It is strongly recommended to monitor the temperature of the heatsink, triacs and SSRs with NTC resistors in this case. The hydrocontrol provides the necessary AD inputs.

1 x phase angle Triac 24 A

2 x static triac 24 A

2 x SSR 48 A

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168 A per phase

Result: 3 triacs and 2 SSRs per phase, or 9 triacs and 6 SSRs in total

Heat sink calculation

The standard passive heatsinks which I use:

RAD-A4291/1000 L:1000mm;W:165mm;H:35mm;Aluminium STONECOLD from www.tme.eu

These can handle around 1.3 A per cm. This is with lots of safety margin for hot environment, degraded heat flow between triac and heat sink, unexpected overcurrent etc.