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Posted By Topic: 3 phase meter reading

Mar 02 2020 22:15

Just wondering if anyone here can help. I have an industrial site with 3 phase ct metering.
Meter is read every 30 minutes yet units are in kw/h. Can anyone explain how this is done ?

Mar 02 2020 22:38

You pay for units. 1 kw in 1 hour that is 1 unit (1 kWh). If you use1000 units in 30 minutes that is 1000 units. Use the same amount for the next hour and you use 2000 units. Or 2000 kWh. The fact they read everything 30 minutes is irrelevant. They can read every minutes if they wish. You only get charged for units that you use.

Mar 02 2020 23:01

Thanks for quick reply. I guess the bit Im struggling with is how a 30 min reading is converted to an kw/h. To me the only way to to convert to a kw/h reading would be to double it otherwise it can only be a kw/ 1/2 hr reading

Mar 03 2020 07:18

your monthly bill will also be in kw'h it's just done using maths.if you use 10kw's in an hour (10 kw/h)then using maths you use 5 kw/h in half simply

Mar 03 2020 08:49

As pawpaw said, the rfequency of reading is not relevant to the amount measured.

The meter is keeping a running total of usage. The reading is just the total-to-date at that moment. When read every half-hour the differences between readings will be smaller, but that's the only real difference between modern half-hourly readings and the older monthly readings, or 2-monthly readings with estimates between.
That and the fact they can track when peak loads are.

Mar 03 2020 12:33

One gentleman I spoke to said the meters were like a car speedo and that the readings were a snapshot every 30 min. If this is true then the figures dont work. If you do 5 km/h for 30 mins and a further 5km/h in the next 30 min. How far have you travelled in an hr. My maths says its 5km in an hr

Mar 03 2020 13:44

I should have spotted the error first time; those readings are not "kW/h" (kilowatts per hour), they are kilowatt-hours (kilowatts multiplied by hours).

And the car analogy isn't with a speedometer (how fast you are going), it's with the odometer (how far you have travelled). It doesn't matter how often readings are taken, each reading is just distance-to date (for the car) or energy-to-date (for the electricity.

The equivalent of the speedo would be a value in kW; telling you how fast you are using power, but not how much you have used.

Mar 03 2020 14:48

He was referring to the speedo as if it was the odometer then the meter would simply record in kw

Mar 03 2020 22:00

Depending on the capacity of the site reflects on the metering. Usually any site in the category 2 classification (150amps-500amps) is NHH (non half-hourly) metering and sites larger in capacity Category 3 (500-1200A), and Category 4 (1200-2000A) are HH (half-hourly) metering.
The tariff for half hourly metering is TOU (time of use). There are TOU sites ie HH metered category 2 sites buts it’s not usually, just a Night/Day tariff in most cases.
The energy consumed in HH metered sites are downloaded every half hourly period. It’s important to extract this data for large sites as tariff prices change as per peak loading for example. If you were to record a value at half hourly marks it will be relative for consumption used that half hourly period. It’s very important for those half hourly downloads by the DA’s (data admins) if they cannot get that data they will have a metering technician there pretty quick to sort out the signal (usually) so reads can continue.

Mar 04 2020 00:00

To add to this, the meters measure the power hundreds of times per second and add it to the counter. The value of the counter is reported every half hour, or every day, or every month.

This is so that they can pick up short spikes that might consume a lot of power in a short amount of time, and also so that you can't have the BMS switch everything off for half a minute every hour so the load is low when the meter checks...

The little flashing red light could be helpful. Depending on model, it typically flashes for every 1/800th or 1/1000th of a kWh. It's kind of like your wheel spinning perhaps a thousand times for every mile on the odometer. No matter how fast or how slow, it's the total distance that matters.

Your time-of-use metering is like checking the odometer every time you fill up: the difference between the new reading and the last one is how much you've used in that time period.

Mar 04 2020 07:20

The most common HH TOU metering asset is the EDMI MK10E meter, these had a pulse output of 5000imp/kWh, trying to count pulses would be virtually impossible because the flashes will be near on constant. Also remember these meters also record REACTIVE power kVArh which is also billed to the consumer.

Mar 04 2020 09:49

The metering im referring to was on our old supply and was metered on the 11kva side. We had to install a new supply which has the above meter. Hopefully this will be a little easier to understand. Old data for example was sent in 48 readings for a day. Pretty simple if it was in KW to work out. However data is in KW/h. So I have 48 readings in KW/h. Thats the bit Im struggling to understand. To me these readings need to bought back to a 24hr format as you cant have 48 hrly readings in a day. Cheers for everyones input.

Mar 04 2020 10:55

It's not kW/h (killoWatt / hour), it's kWh (killoWatt x hour).

Go back and reread the others' post again.


Mar 04 2020 10:57

err, "kilo", rather.


Mar 04 2020 11:01

A kiloWatt-hour is a quantity of energy. It's an alternative to Joules. 1 kWh == 3.6 MJ.


Mar 04 2020 20:45

An important point to be aware of is that the majority of EDMI Mk10E meters installed do NOT have the CT Ratio applied to the meter.

The values displayed on the LCD are Not used in calculating your power bill.

HHR meters are read by the DA on a schedule hat depends on the Category of metering. Higher Categories get read more often.

Even NHH meters report usage in half hour blocks. The data is treated differently in the back office (Day/Night versus Time of Use) for example.

Category 2 metering can be either HHR or NHH.