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6.0 MEASUREMENTS

Basic measurement quantities are calculated and updated every 100 ms. These

quantities include RMS Amperes and RMS Volts, Watts, VARs, VAs, Power Factor, all

harmonic-based measurements (such as fundamental-only quantities), Energy, and

Frequency, and Phase Angle.

Note: For all of the following measurements, it is important to keep in mind that the

specific protocol used to access the data may affect the data that is available, or the

format of that data. No attempt is made here to describe the method of accessing

measurements - always check the appropriate protocol manual for details.

6.1 Changing Transformer Ratios

The M650 has the capability to store values for Current Transformer (CT) and

Potential Transformer (VT) turns ratios. The VT and CT values are factory set to 1:1

CT and 1:1 VT. These values can be entered into the M650 over the network or via

front display buttons or web page, and will be stored in internal non-volatile memory.

All measurements are presented in primary units, based on these ratios. Please note

that the value entered via the front display should be the result of the division of the

primary value by 5. For example for a ratio of 6000:5, you would enter a value of 1200

through the front display. The web interface allows you to choose either 1A or 5A for

the denominator, and the primary value is entered directly. The PT ratio is to 1 when

entering through the front display. The web allows other denominators (110, 115, or

120) to be used. Refer to the appropriate protocol manual for more information on

changing transformer ratios.

6.2 Current

The M650 has three current inputs, with an internal CT on each channel except in the

case where external split-core CTs are used. These inputs can read to 2x nominal

(2A

RMS

for 1A input, 10A

RMS

for 5A input (symmetrical)) under all temperature and input

frequency conditions. No range switching is used, allowing a high dynamic range.

The current signals are transformer coupled, providing a true differential current signal.

Additionally, a continuous DC removal is performed on all current inputs. Instrument

Transformer Ratios can be entered for each current input, as described above.

The average of the 3 current phases ((Ia + Ib + Ic)/3) is also available.

6.2.1 Residual Current

The M650 calculates the vector sum of the three phase currents, which is known as

the Residual Current. The Residual Current is equivalent to routing the common

current return wire through the neutral current input on systems without separate

current returns for each phase.

Novatech Bitronics 50 Series User Manual

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