118
Functional Description
at a particular point in a power distribution system, along with suitable time synchronization
fields and other information.
This information is available in real time, and is based on the
measured fundamental voltage, current, and phase angle described above, at a variable rates based
on system frequency. There is a measurement delay due to the data acquisition delay of 50 ms,
signal processing time of approximately 15 ms, and data transfer time which depends on the data
rate.
11.20
Phase Balance
The 1133A measures phase balance by calculating the symmetrical sequence components (positive,
negative, and zero sequence) for the three-phase voltage input. Normally, if the unit is connected
properly, the positive-sequence voltage will be equal to the line voltage and the negative- and
zero-sequence voltages will be approximately zero.
In the event that a user-specified limit on
the imbalance (See “Triggering,” later in this section) is exceeded, an event will be recognized.
In addition, the sequence components are averaged over a user-specified interval (typically 10 or
15 minutes) and may be logged if desired. These calculations are performed using the voltage
magnitude and phase information, at the rate of 20/second.
11.21
Load Balance
Load balance is calculated in much the same way as phase balance, except on the customer’s load
current. Both of these measurements may be used to identify serious power system problems, such
as a dropped phase, which could cause serious damage to both the utility’s and the customer’s
equipment.
11.22
Flash Memory and Event Logging
The Model 1133A has 32 megabytes of standard flash memory for recording, including registered
quantities, event data and system status events. Registered quantities are recorded on a fixed
schedule and may include many more items than a typical energy meter, including just about any
function the instrument can measure. The event data are logged on the occurrence of an event
designated to initiate logging. System status is used for advanced monitoring and control of the
operation of the 1133A and the system node to which it is connected.
Events are defined as any measured quantity exceeding a user-specified threshold, an external
trigger, or an internal state of the 1133A (low flash memory, for example). In addition, an event
may trigger a dial-up modem call to be initiated, reporting the event; and/or a relay contact may
be closed (or opened).
There is a great deal of flexibility as to what may be recorded in flash memory at the time an
event is recognized. Recorded information may include any of the following:
◦
Time of event
◦
Type of event
◦
State of measured quantities
◦
Pre- and post-event data
◦
Any of the measured quantities - e.g. voltage, power, waveform, etc.
