Vanguard CT-7500 - Manual (Page 7)

MODEL CT-7500 OPERATING INSTRUCTIONS
Rev 2 Jan 2001
1
1.0 Introduction
The Model CT-7500 is a microprocessor-based digital time-versus-travel Circuit Breaker
Analyzer with a special on line test mode. This on line test mode (Quick-Shot mode) allows the
user to capture breaker contact close time and contact open (clear) time while the breaker is still in
service. In the off line test, the Model CT-7500 fully analyzes utility circuit-breaker performance:
contact time, stroke, velocity, over-travel, bounce-back, and contact wipe.
Contact-motion analysis includes: Open, Close, Open-Close, Close-Open, and Open-Close-
Open. A timing window is selectable between 1-second or 10-second periods. The 10-second
window allows timing of long events (e.g., circuit switcher contacts).
The CT-7500 is available in three models:
„ CT-7500-3; three contact channels.
„ CT-7500-6; six contact channels.
„ CT-7500-12; twelve contact channels.
All the CT-7500 models have the following input:
„ Three Digital Travel Transducer Input channels.
„ One Analog Voltage Monitor Input channel.
„ One Digital Voltage Monitor Input channel.
„ One Trip/Close current monitor channel.
There are two modes of operation for the CT-7500: Stand Alone Mode and Computer Control
Mode. This manual will focus on the CT-7500 Stand Alone Mode. The Computer Control Mode is
covered under the CT-7500 PC software manual.
2.0 CT-7500 Description
2.1 On-line Timing (Quick-Shot) mode
A clamp-on AC current probe connected to the breaker bushing CT lets the CT-7500
measure breaker switching time (while the breaker’s still in service). The CT-7500 can time an
OPEN operation by sensing the time when the OPEN coil is energized until the bushing CT
current returns to zero. CLOSE time is detected when the close coil is energized until the bushing
CT current is detected.
This “Quick-Shot” mode provides a quick way to diagnose breaker performance and savings in
maintenance cost.
2.2 Time-Versus-Travel Circuit Breaker Analyzer Mode
The CT-7500 applies a 35Vdc voltage to each of the contact channels. This test voltage is
sensed by an analog to digital converter (A/D) to determine the state of the contact (close, or
open, or insertion resistor). The CT-7500 records the A/D reading at a 10 KHz rate, and stores
these readings in memory. The contact/resistor time is then derived from data stored in memory.
The CT-7500 uses three up-down counters to sense the breaker’s transducer reading. The
CT-7500 travel transducer employs an optical encoder to send quadrature signals to the CT-
7500’s counters. With the use of the digital transducer and counters, the user never has to set up