Instrument power specifications must take into account not only instrument requirements, but also the context, which in this case means Chilean standards and practices at other telescopes on Cerro Pachon, ie Gemini. CTIO will be providing input to the project from the operations perspective on related issues such as power for computers, building (dual voltage), lighting (220V, proximity detection), and heavy equipment (381V), grounding.

Supplied by power grid:

380 V 3-phase star, 50 Hz. Check the rumor that the Gemini transformer will be sufficiently over-specified to also carry SOAR.

Line frequency:

50 Hz Chilean standard only. Instrument power supplies and electrical equipment (motors, transformers, etc) are readily available in the USA with 50 Hz ratings. Frequency converters are very expensive and unnecessary.

Instrument power:

The KVA rating defines what current the circuit can supply but does not authorize the instrument to dissipate this number of watts on a continuous basis. Heat dissipation must be minimized to control the cost and size of the heat extraction system.

Instrument power is generally dominated by detector electronics for science, guiding and wavefront sensing. (Most mechanisms with the exception of tip-tilt and deformable optics operate at low duty cycle.) These tend to scale with peak readout bandwidth, and to be independent of telescope aperture. Thus we strongly recommend adopting the Gemini standards for the power supplied to each instrument since we expect the power dissipation to be comparable.

While power saving technologies are helping reduce power consumption our demand for larger focal plane arrays and faster readouts tend to increase the power requirements so predicting future power requirements is difficult. We must err on the safe side at least when specifying power ratings of circuits.

Color coding and labeling

Uninterruptible, isolated and raw power outlets must be distinguished both by labeling and color coding: color coding alone is not sufficient. Voltages shall be distinguished by connector (in)compatibility.

Power wiring colors

Black Line/active/hot White Neutral/return Green Earth

Fixtures

Instrument and computer power outlets are to comply with Gemini ICD 1.9/3.6, section 3.3.2.

To implement safe and reliable dual voltage power, we need to identify a supplier of robust 220V receptacles, and especially plugs and outlet strips. The quality of average Chilean electrical fixtures has historically been very poor. This is changing in the current economic climate. (Eg: non-reversible 2 pin plugs going by the local name "magic".)

National standards

120V Adheres to US national electrical wiring code ("120V" encompasses a 12% range, such that it is also referred to as 110V or 115V). 220/381V Adheres to Chilean electrical wiring code.

Load factor & Harmonics

Standards have been developed relatively recently in Europe (and the USA?)to ensure that line voltage waveforms supplied to the consumer are acceptably clean, and conversely that the consumer's equipment does not contaminate the line by drawing high frequency or highly non-sinusoidal load currents. The motives relate to both power distribution efficiency and conducted noise. Appropriate specifications and certification procedures should be adopted for...

- the load factor presented by instruments in order to limit the current for a given KVA.

- the high harmonics of the current drawn by instruments in order to limit transformer losses and distortion of the line voltage waveform.

- the high frequencies impressed on the power lines by equipment.

We strongly recommend that critical areas such as raw power to detector systems and computers be filtered by resonant isolation transformers. Separate isolation transformers should be used on each circuit to minimize the contamination of one subsystem's power by another.

Roger and Gale