(4Q Issue) -- APQI Case Studies

Equipment PQ Performance Standards Dean Arnold S. Sempio and Rolan S. Mercado MERALCO

In the days before computers, most electrical loads consume power linearly – that is, the current drawn traces the voltage waveform. Today, the widespread use of electronics in the industries has created a demand for better power quality as electronic equipment are not as tolerant of voltage waveforms and events as the old loads. Ironically, these electronic equipment are nonlinear loads that draws non-sinusoidal current and causes voltage waveforms to be distorted.

Various “ride-through capability standards” were made in order to aid manufacturers and the electric utilities in establishing a common viewpoint of how electrical equipment would behave on certain voltage events. Manufacturers design equipment based on the “compromised” levels between the equipment capability and grid performance of the utility.

Developed in the 1970s (originally, the CBEMA, Computer and Business Equipment Manufacturers Association) and revised in 2000, the ITIC (Information Technology Industry Council) curve is now one of the most common tools available to engineers; using the ITIC curve can help point map the sensitivity of electronic equipment or help improve the performance of a power distribution system. Here is the ITIC curve:

The ITIC curve shows two lines representing the upper and lower limits. In the upper limit, voltages up to 500% of the nominal may not cause damage to IT equipment IF the duration is below the curve’s specified time limit. This category includes voltage transients as well as voltage swells.

The SEMI F47 standard is another voltage sag susceptibility curve which is intended specifically to semiconductor manufacturing equipment, which include etch equipment, thermal equipment and ion implant equipment.

SEMI F47 “Specification for Semiconductor Processing Equipment Voltage Sag Immunity” defines the voltage operating limit that semiconductor processing equipment can operate through without stopping its operation. Voltage values below the SEMI F47 curve may cause the semiconductor equipment to malfunction or stop operating altogether due to lack of the required operating energy.

These tools are incorporated into several power monitoring equipment output as aid to the engineer’s study on voltage tolerance of equipment as well as providing a list of disturbances in the power grid being monitored. The usefulness of these tools is illustrated in the case study below: Semiconductor Processing Equipment Problem A semiconductor manufacturing company has requested a power quality monitoring due to “voltage fluctuations” (i.e. voltage sags) affecting the operation of their equipment, particularly their tunnel furnace. A Power Quality monitoring device was installed at the panel serving the customer equipment.

PQ Monitoring Results The data from the monitoring showed that the voltage regulation, voltage unbalance and voltage harmonic distortion to be within industry parameters. However, the data from the monitoring

also captured several voltage sags events. The characteristics of the voltage sags (voltage magnitude and duration) were plotted in the SEMI F47 curve:

According to the company, the tunnel furnace has stopped operating more than 7 times during the monitoring period; much more than the three events that violate the SEMI F47 curve. This suggests that the equipment is much more sensitive to voltage sags as it should be.

Solution A UPS unit was recommended to increase the voltage sag tolerance by providing power to the equipment controls during a voltage sag event. The customer was surprised when the equipment vendor pointed out that there is a UPS option for their equipment, the customer need only to specify for the UPS option to be installed.

Variable Speed Controls Problem A customer in the manufacturing business has complained that frequent voltage sags has reduced the operating time of a vital equipment being controlled by a variable speed drive.

Power Quality monitoring A Power Quality Analyzer was installed at the panel serving the customer equipment. The data from the monitoring shows that the voltage regulation, voltage unbalance and voltage harmonics

were all within industry limits and should pose no problem to the VSD operation. However, the following voltage sags were captured by the equipment:

Most of the sags captured were verified by the customer as enough to cause the stopping of the VSD operation.

Solution The data showed that most of the voltage sags were “shallow�; the voltage values went down to only 88% from their nominal values. A cost effective solution was recommended as the PQ engineer observed that the equipment is being sole load of a secondary transformer. It was recommended that the transformer’s tap setting be changed to increase the secondary voltage.

The increased voltage will still be within the operating limits of the VSD but will increase the stiffness of the electrical system against voltage sags.

Conclusion The usefulness of equipment operating standards is not limited to utilities and equipment manufacturers. Ultimately, the equipment users will also benefit from the increased reliability and use of equipment that passes these operating standards.