# Glossary of electrical machine terms

The following list comprises many terms used in the field of electrical machine design. Click on a glossary term for more details.

Advance angle | In a brushless DC (BLDC) machine, the advance angle defines the timing of the current commutation in relation to the rotor position. |

Airgap diameter | Diameter from the middle of the airgap to the middle of the airgap on the opposite side. |

Airgap thickness | Distance between the rotor surface and stator surface. |

Average conductor length | Average length of a conductor including the length of the end-winding. |

Boundary conditions in finite element analysis | Discussion of different possible boundary conditions and their significance |

Brushless AC machine | Discussion about how how to choose the d- and q-axis components of the sinusoidal three-phase currents feeding the BLAC machine. |

Brushless DC machine | Discussion about star- and delta-connected BLDC machines. |

Coil span | The coil span is the distance between one conductor of a certain phase and the corresponding return conductor. |

Concentrated winding | In Emetor, a winding is called concentrated winding when the number of slots per pole per phase is fractional and strictly lower than 1. |

Conductor losses | Conductor losses result from Joule heating of electrical currents in the conductors of electrical machine windings. |

Delta Star connection | Two different possibilities to connect the three phases |

Demagnetization | Loss of magnetization of permanent magnets due to high temperatures or inappropriate operating conditions. |

Electrical frequency | The electrical frequency is the fundamental frequency of the current and voltage at the machine terminals measured in [Hz]. |

End-winding leakage inductance | Leakage inductance of the winding end-turns. |

Fractional-slot winding | In Emetor, a winding is called fractional-slot winding when the number of slots per pole per phase is fractional and superior to 1. |

Integer-slot winding | A winding is called integer-slot winding when the number of slots per pole per phase is an integer. |

Lamination thickness | The thickness of the iron lamination sheets varies between about 0.05 and 0.5 mm in most electrical machines. The choice of lamination thickness depends on a balance between performance and cost. |

Least common multiple between the number of poles and the number of slots | This value is the lowest number that is a multiple of both the number of poles and the number of slots. It is an indicator for what levels of cogging torque one can expect. |

Machine length | The active length of the machine, i.e. the length of the stator and rotor iron cores. |

Magnet angle | The magnet angle is provided in electrical degrees and defines the width of the surface-mounted permanent magnets. |

Magneto-motive force | The magneto-motive force, often abbreviated as MMF is any physical driving force, such as a current in a coil, that produces magnetic flux. |

Magnet radius | Surface radius of a breadloaf magnet. |

Magnet thickness | The magnet thickness is a geometry template parameter in Emetor that defines the thickness of the permanent magnets in their middle. |

Magnet width | Width of a breadloaf magnet. |

Mechanical speed | The mechanical speed is the speed of the rotor measured in [rpm] or [1/s]. |

Negative magnetic periodicity | Machines with concentrated windings and a negative magnetic periodicity can be simulated much faster due to the fact that the simulated cross-section can be cut in half. |

Number of conductors per slot | Defines how many conductors that are placed in one slot. |

Number of parallel paths | The winding of an electrical machine can be split into a certain number of parallel paths in order to adjust the voltage and current ratings to those of a specific supply. |

Number of slots per pole per phase | The number of slots per pole per phase determines how the winding layout is arranged. It is also disclosing information about the winding factor and its harmonics. |

Number of winding layers | The number of layers indicates the number of different coils in a slot. |

Number of winding symmetries | The number of winding symmetries indicates the number of rotational symmetries in the winding layout. It indicates also the machine periodicity. |

Phase resistance | Electrical resistance of the winding conductors in one phase. |

Permanent magnet tolerances | Permanent magnets do not only vary in magnetic moment and magnetization direction, their properties may also differ considerably depending on the size and shape of the actual magnet. |

Phase voltage | Voltage across the phase winding. |

Power factor | Ratio between real power and apparent power. |

Reduction of coil span | This value expresses the reduction of the coil span compared to full pitch. The higher the reduction of coil span, the shorter the end-turns of your winding. |

Shaft diameter | The shaft diameter in Emetor is the diameter of the hole in the iron laminations that contains the shaft. |

Slot fill factor | Ratio between the cross-sectional area of all conductors in one slot and the entire slot area. |

Slot opening width | The slot opening width is the distance between two tooth tips. |

Stacking factor | The stacking factor is the ratio of electrical steel along the axial length of the iron core. |

Temperature of conductors | The conductor temperature is an input necessary in order to calculate the conductor losses, and hence the machine efficiency. |

Tooth width | Width of the stator teeth. |

Torque ripple | The torque ripple in electrical machines is caused by many factors such as cogging torque, the interaction between the MMF and the airgap flux harmonics, or mechanical imbalances, e.g. excentricity of the rotor. |

Unbalanced winding | An unbalanced winding has a combination of number of poles and number of slots that does not allow to arrange the coils in such a way that they produce a symmetrical system of equally time-phase displaced emf's of identical magnitude, frequency, and waveform. |

Winding factor | The winding factor for a specific winding expresses the ratio of flux linked by that winding compared to flux that would have been linked by a single-layer full-pitch non-skewed integer-slot winding with the same number of turns and one single slot per pole per phase. The torque of an electric motor is proportional to the fundamental winding factor. |

Winding layout | The winding layout is the arrangement of the coils of each phase in the slots. |