Most transmission lines laid by Kyushu Electric Power Co., Inc. (KEPCO), Fukuoka, Japan, run through mountainous areas. Trees growing below the lines increase the possibility of line outages when they come into close proximity with such lines.

A portion of line maintenance work involves determining the exact locations of trees near lines and the measurement of the separation between lines and trees. Related research and measurements are strenuous and time consuming, requiring workers to haul heavy equipment up steep mountain roads and measure trees near lines from locations with poor footing.

Faced with this situation, the KEPCO Research Laboratory, in a joint effort with the NEC Corp., developed the Heliborne Separation Measuring System. Designed to improve and bring efficiency to maintenance work, it employs a measuring unit mounted under a helicopter to measure the separation between lines and trees. A practical system should be complete around the end of 1997.

Separation Measurement The system ultimately functions to determine the separation between lines and trees by first determining the distance from a pulse laser measuring apparatus to target objects.

- A laser generator sends a laser pulse through a light transmitting telescope toward targets below. The same pulse is also sent to a flip flop (F/F) circuit through a light detector. This causes a gate to open. - Once the gate opens, clock pulses are sent to a counter. The counter counts the number of clock pulses. - The laser pulse, reflecting off targets, returns through the light-receiving telescope and light detector to the F/F circuit as a reflected pulse. The gate then closes. - Once the gate has closed, clock pulses cease.

Separation Measurement Method The system determines the locations of trees and measures the distance by which they are separated from lines over a wide range. It uses a mirror to disperse laser pulses. Figure 3 shows the separation measuring method used. The principle is as follows:

- The pulse laser measuring apparatus' pulse laser sends pulses straight downward, relative to its line of flight. - Laser pulses are transmitted in the shape of a 45 deg semicircle from the helicopter so that all targeted lines and trees may be measured. - The measuring unit receives laser pulses reflecting off lines and trees and measures the range (r) and direction ((3 ) of these targets relative to it. - The coordinates of lines and trees are calculated based on the measurements with the formula (x, y) = (r x cos (3, r x sin (3 ) - The separation between lines and trees is calculated based on the measured locations of trees and lines.

The above principles hold true only when the helicopter flies at a constant speed in an ideal flight pattern without oscillation. To correct measurements, the device employs a monolithic ring laser gyro accelerometer (MRLG) that records the helicopter's behavior, angle and acceleration.

Outline of the System The system consists of two portions: a heliborne portion and a processor for data analysis. The measuring unit located underneath the helicopter comprises a pulse laser measuring apparatus, an MRLG and a visual camera. Additionally, an on-board data recorder records separation and helicopter flight data on 8 mm data tapes. The visual camera films lines and their surroundings and records this on 8 mm videotapes.

The processor has work stations capable of processing images. Data processed may be used to show separation and tree location by line span (the area between towers). Filmed images may be converted to still ones. A mouse click on a specific location will reveal specific separation data. A mouse click on any of the lines will reveal the separation between that line and concerned trees.

Cost Reduction With the system, lines extending 62 miles (100 km) can be surveyed during a two-hour flight. With personnel costs high in Japan, this performance cuts several million dollars per year off the cost of manual survey work. Data, after being processed by the processor, is sent to KEPCO's Transmission Section on MO disks. Personal computers belonging to the section display the results and output hardcopies. Any separation from increased line dip due to temperature rises and horizontal vibration due to wind is automatically calculated. The computers produce related documentation. Conventionally prepared documents are based on manual site survey results by manual operation. The efficiency of management work is also increased.

Programs specifically designed for the system will be upgraded to increase the processing speed and improve the visual comprehensibility of images. Steps toward practicality will be taken toward the end of 1997.

Toshio Motomura is assistant research manager, Power Engineering Research Div., Kyushu Electric Power Co., Inc., Fukuoka, Japan. He graduated from the Department of Electric Engineering, Faculty of Engineering, Nagasaki University in March 1979 and joined KEPCO in April of that year. He achieved his current position in July 1995.

Masakazu Hirao is a researcher in the KEPCO research laboratory. He graduated in 1987 from the Department of Electric Engineering, Kitakyushu Technical College and joined KEPCO in April 1987. In August 1995 he was promoted to his present position.