Hi everyone, I have a few questions on 3 phase power in SA. I couldn't find any straight answers on google.

1. Why do the loads on a 3 phase power system need to be "balanced". Is this only to avoid tripping/overloading any single phase?

2. Does balance mean, at any given time, the loads are at somewhat equal power draw across all 3 loads? Or does it simply mean that each phase does not exceed a certain power draw, and certain phases can remain idling?

For example, I have geysers and aircons on phase 2 and 3, and all my main plugs, lights, appliances etc on phase 1. Phase 1 is going to in use 90% of the time, as the geysers operate on timers, and aircons are hardly in use, only when required. In this case, phase 1 gets the most constant use, and phases 2 and 3 are mostly idle. But if I were to look at power draw over say a month, the geyers would obviously add up.

3. How is the electricity bill determined in 3 phase? Is it simply a case of the power usage for each phase being calculated and added together?

4. What are the consequences of unbalanced loads? I have heard that you will be charged more if your loads are unbalanced, or is this nonsense?

5. Based on google searches, unbalanced loads mainly affects performance of 3 phase equipment such as motors etc. I do not have any such equipment. My pool pump states single phase motor. Are there are other consequences?

6. If I were to get a single phase inverter and solar setup in a 3 phase setup, I assume its fine if all I am worried about is powering items on phase 1?

7. Is it easy to get prepaid meters for 3 phase setups? I am based in JHB and currently a COJ customer. Are there any issues with having prepaid and a solar setup (assuming no grid feedback) ?

 

4 hours ago, sam_i_am said:

Hi everyone, I have a few questions on 3 phase power in SA. I couldn't find any straight answers on google.

1. Why do the loads on a 3 phase power system need to be "balanced". Is this only to avoid tripping/overloading any single phase?

2. Does balance mean, at any given time, the loads are at somewhat equal power draw across all 3 loads? Or does it simply mean that each phase does not exceed a certain power draw, and certain phases can remain idling?

For example, I have geysers and aircons on phase 2 and 3, and all my main plugs, lights, appliances etc on phase 1. Phase 1 is going to in use 90% of the time, as the geysers operate on timers, and aircons are hardly in use, only when required. In this case, phase 1 gets the most constant use, and phases 2 and 3 are mostly idle. But if I were to look at power draw over say a month, the geyers would obviously add up.

3. How is the electricity bill determined in 3 phase? Is it simply a case of the power usage for each phase being calculated and added together?

4. What are the consequences of unbalanced loads? I have heard that you will be charged more if your loads are unbalanced, or is this nonsense?

5. Based on google searches, unbalanced loads mainly affects performance of 3 phase equipment such as motors etc. I do not have any such equipment. My pool pump states single phase motor. Are there are other consequences?

6. If I were to get a single phase inverter and solar setup in a 3 phase setup, I assume its fine if all I am worried about is powering items on phase 1?

7. Is it easy to get prepaid meters for 3 phase setups? I am based in JHB and currently a COJ customer. Are there any issues with having prepaid and a solar setup (assuming no grid feedback) ?

 

Each phase is measured and equipment are designed for this current. You thus don't want to go higher while other phases are lower. Also you get neutral current flowing while if balanced no neutral current flowing from the star of a transformer. 

By not balancing it more difficult for the supplier to provide the power. If your 1st phase carried less power some will be available for the next customer. 

For smaller users each phase is measured even if it might be a single 3 phase meter 

Large consumers are indeed charged for the out of balance load for the reason given earlier. 

No problem with the pool motor if used on any phase 

The solar side follows the inverter. Thus 3 phase inverter if PV must be 3 phase. There are pros and cons for solar on 1 or 3 pH. I would lean to single phase. If no 3 pH equipment single pH is cheaper. 

Last one I leave for CoJ members. 

5 hours ago, sam_i_am said:

Hi everyone, I have a few questions on 3 phase power in SA. I couldn't find any straight answers on google.

1. Why do the loads on a 3 phase power system need to be "balanced". Is this only to avoid tripping/overloading any single phase?

2. Does balance mean, at any given time, the loads are at somewhat equal power draw across all 3 loads? Or does it simply mean that each phase does not exceed a certain power draw, and certain phases can remain idling?

For example, I have geysers and aircons on phase 2 and 3, and all my main plugs, lights, appliances etc on phase 1. Phase 1 is going to in use 90% of the time, as the geysers operate on timers, and aircons are hardly in use, only when required. In this case, phase 1 gets the most constant use, and phases 2 and 3 are mostly idle. But if I were to look at power draw over say a month, the geyers would obviously add up.

3. How is the electricity bill determined in 3 phase? Is it simply a case of the power usage for each phase being calculated and added together?

4. What are the consequences of unbalanced loads? I have heard that you will be charged more if your loads are unbalanced, or is this nonsense?

5. Based on google searches, unbalanced loads mainly affects performance of 3 phase equipment such as motors etc. I do not have any such equipment. My pool pump states single phase motor. Are there are other consequences?

6. If I were to get a single phase inverter and solar setup in a 3 phase setup, I assume its fine if all I am worried about is powering items on phase 1?

7. Is it easy to get prepaid meters for 3 phase setups? I am based in JHB and currently a COJ customer. Are there any issues with having prepaid and a solar setup (assuming no grid feedback) ?

 

1. Balanced loads reduce volt drop on the reticulation system because there is no neutral current.

2. Balanced means the loads are at equal power draw across all 3 phases.

3. To my knowledge most small three phase meters add the energy on all three phases.

4. You will pay slightly more for energy if there are more losses on an unbalanced system downstream from the meter. But this comes down to heating of the neutral conductor.

5. More losses cause more volt drop and lower supply voltage. Overloading your neutral could make it burn off and then some single phase loads will get 400V. Single phase equipment are weak on a size and weight basis. They also don't last as long as three phase equipment.

6. You can use a single phase inverter for essential loads on a three phase system.

7. Keep the mechanical meter, export power and save the country from load shedding.

Thanks guys, appreciate the feedback!

I have received data from a 3 phase logger installed at my appointment building but need help to analyze the data. The data was provided by a solar guy. Solar is too expensive and I want ro consider another power supply option like a generator, but limiting the run rime. I want to use the data to understandthe peak load times. Who can help me analyze this data?

When you run appliances across 3-phase, balance simply means the load should be shared as evenly as possible across all three phases. If too many heavy appliances sit on one phase while the others are light, that side can draw more current and trip sooner.

Geysers and air-cons are normally high-load devices, so if they are on phase 2 and 3, it’s normal to see slightly higher usage there. Ideally, electricians try to distribute things like plugs, lights and big appliances so one side isn’t overloaded. It doesn’t have to be perfect every second, but the goal is that over time the phases carry similar load.