Installation manual

© 2014 EcoInnovation Ltd (NZ) Page 84
6.9. Installation example
A potential customer wants to purchase a PLT80 PowerSpout hydro turbine that will
generate up to 1000 W on their site data. The rated voltage is 80 VDC and the unloaded
voltage (Voc) is 240 VDC. They intend to use a Midnight Classic 250 controller and the aux
relay will be used to turn on a 327 W water heater (1500W at 120 V element is used) with
surplus energy not needed to charge the batteries. There will be a 5kW inverter in the
system and two x 48 VDC battery strings each of 400 amp hours. The advanced calculation
tool has sized the cable for you at 6mm
2
for 3% power loss in the cable.
Question: What is the size of breakers needed DB1-DB5?
Answer:
In all cases the breaker must protect the wiring of the circuit, so the wiring should
never be smaller than the breaker's rated current.
DB1 and DB2.
Cable amps=12.5 (1000/80) and the short circuit amps = 20 (listed on the turbine nameplate).
Breaker rating should be at least 25% more than rated amps.
Minimum breaker size = 1.25 x 12.5 = 15.6 amp.
Hence a 16 amp breaker is selected.
In the event of a 20A cable short the breaker may trip, but a larger breaker would also be
acceptable in this case, since the short circuit current cannot overload the 6mm
2
cable.
DB3
As the MC250 is rated for 63 amps, you can therefore fit a 63 amp breaker. (In this case
make sure the battery wiring is suitable for 63 amps.)
Or if you prefer a breaker rated at least 25% more than the output amps of the MPPT unit in
operation = 1.25 *1000/48 = 26 amp. A 32 amp breaker is the smallest size above 26 amp.
DB4
As the diversion element is rated for 327W, the minimum breaker size is 1.5 x 327/56 = 8.75
amps, so a 10A or larger breaker should be used (within the rating of the battery cable). Note
that we use 56 V and not 48 V for diversion load calculations.
DB5
The inverter is rated for 5kW but can surge to 9,000W. Hence 160 amp inverter fuse/breaker
is a good choice. A 160 amp HRC 3-pole holder was used to do this just under the inverter as
this was more cost efficient than a 160 amp breaker.
Main HRC battery fuse
The battery bank will not be earthed in this case, so both poles have to
be fused. As we have 2 battery strings these also need to be combined
and separately fused.
Two 3-pole HRC holders are used to combine both strings and top
combiner links are fitted to both holders as shown. The spare positions
are used to break the incoming hydro DB2. A copper
link (to replace the fuse) is put in the spare position
and a 16 amp breaker is installed for DB2. The breaker
can be used to check open circuit voltage and in some
cases might be needed to protect the cable from
overload.
Opening any one HRC holder will completely shut
down the system.
The final system looked like this.