|
| PQ issues | Causes | Category | Magnitude (pu) and duration | Effects |
|
| Voltage dip/sag | Start of huge loads, loading of grid, variations in supply voltage, inrush current, faults, and irregular connection | Instantaneous | 0.1–0.9 | Motor overload or decay, lock-up, and data inaccurate |
| 0.5–30 cycles |
| Momentary | 0.1–0.9 |
| 30 cycles–3 sec |
| Temporary | 0.1–0.9 |
| 3 sec–1 min |
|
| Voltage swell/rise | Stop/start of large loads, variations in supply voltage, inrush current, and irregular connection | Instantaneous | 1.1–1.8 | Loss of data, damage to equipment, lock-up, and data inaccurate |
| 0.5–30 cycles |
| Momentary | 1.1–1.4 |
| 30 cycles–3 sec |
| Temporary | 1.1–1.2 |
| 3 sec–1 min |
|
| Transient | Stop/start of large loads, lightning, snubber circuits, and incorrect connection to the transformer | Impulsive | Nanosecond | — | Electrical equipment interference, loss of data, flickering of lights, and harm to sensitive appliances |
| <50 nsec |
| Microsecond | — |
| 50 nSec–1 msec |
| Millisecond | — |
| >1 msec |
| Oscillatory | Low frequency | 0–4 |
| 0.3–50 msec |
| Medium frequency | 0–8 |
| 20 μsec |
| High frequency | 0–4 |
| 5 μsec |
|
| Voltage interruption | Insulation failure and disturbance in control | Instantaneous | <0.1 | Disturbance of data processing devices |
| 0.5–30 cycles |
| Momentary | <0.1 |
| 30 cycles–3 sec |
| Temporary | <0.1 |
| 3 sec–1 min |
|
| Harmonic | Nonlinear loads | — | Steady-state | Data unfaithful, lock-up, motors and transformers overheating, and losses in electrical equipment |
| 0–20% |
|
| Voltage fluctuation/flicker | Load switching and supply voltage fluctuations | — | Intermittent | Flickering of light, over and under voltages, and damage to the load-side device |
| 0.1–7% |
|
