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DETAILED OPERATION - Section 4
MTS-1700 SERIES OPERATION AND REFERENCE MANUAL 4-41
CU A002 15A
MANTA TEST SYSTEMS
For example, if the AC line input is 60Hz, and 2nd-harmonic is selected, the frequency display should read
120.0Hz.
4.10.1.2
VARIABLE FREQUENCY REFERENCE MODE.
In this mode, the output voltages and currents are derived from an internal crystal-controlled reference. This
allows the frequency to be varied between 40Hz to 800Hz for testing frequency-operated relays.
To select the variable frequency reference mode:
Press the [FREQ] button until an actual frequency value in Hz is indicated in the upper right corner of the
[MODE/MENU DISPLAY].
To adjust the frequency:
Press [FREQ], and turn the [MODIFY] knob.
The present frequency is displayed on the [VALUE DISPLAY], and on the [MODE/MENU DISPLAY].
The prefault, fault, and postfault frequency can be set independently.
4.10.2 Harmonic Generation
Harmonics of the line frequency may be generated by turning the [MODIFY] knob when frequency modify
is selected, and when the frequency reference is the AC line. The upper right corner of the [MODE/MENU
DISPLAY] annunciates the selected harmonic number.
Note that the phase adjustment resolution is proportional to the harmonic number. The normal 0.25° phase
resolution is reduced to 0.5° for the 2nd-harmonic range; 0.75° for the 3rd-harmonic range; etc.
4.10.3 Dynamic Frequency Testing
In variable frequency reference mode, the frequency in prefault, fault and postfault states can be set
independently. The only restriction is all three settings must be in the same harmonic range.
Some special considerations should be taken into account when the frequency is stepped from a prefault
value to a fault value. This is often performed to test frequency relays.
The MTS-1710 will instantaneously change the frequency from the prefault setting to the fault setting at the
zero crossing of the voltage being monitored. The voltage may be a
Φ
-N or a
Φ
-
Φ
voltage.
If internal timer start mode is selected (see Section 5.3.1), the timer will be synchronized to start at the
moment when the frequency instantaneously changes. This ensures proper timing measurements when
performing this type of test.
The change from prefault to fault state may have occurred up to one cycle before this moment due to the
synchronization to the zero crossing of the voltage.